A legendary question from the toughest exam

Рет қаралды 83,523

23 күн бұрын

This legendary question from India's JEE Advanced test is so hard that most people would not even attempt it. Only 78 out of 161,319 were able to correctly solve it.
solution by kludg
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Other solutions
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• Let \( |X| \) denote t...
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Q11, 2019 JEE Advanced Mathematics Paper 2
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Пікірлер: 350

@ai314159 21 күн бұрын

What makes this question hard is not the math-it's the incredibly confusing wording.

@robertveith6383 21 күн бұрын

* confusing Use the adjective.

@lefthanded3512 21 күн бұрын

Haha, exactly. The problem itself is actually extremely easy if you think about it logically and methodically. The way it’s worded makes it sound like a question only someone with an IQ of 180+ can answer correctly.

@pierreabbat6157 21 күн бұрын

The way I understood the question on reading it, I got the answer 6*57+15*42+20*22+15*7+6*1=1523, where 57 is 15+20+15+6+1.

@ai314159 20 күн бұрын

@@pierreabbat6157 same here

@ayushrudra8600 20 күн бұрын

yeah i solved it pretty easily with contest math background - it was probably just a combination of probability not really being taught in school and the wording

@user-jn4sw3iw4h 20 күн бұрын

With on average 3 minutes per question, through a 6 hour gauntlet the correct answer to this question is "skip, lets see if there will be time left to loop back around"

@mj9765 10 күн бұрын

Most other questions are the same way. The students who answer these have a muscle memory of solving such questions for years, sometimes, unfortunately for a decade! Yes, students start at 8 or 9 yrs of age to prepare for this exam which they take at 18! Very sad!

@user-jn4sw3iw4h 10 күн бұрын

@@mj9765 even with "target audience, is a lot more fluent with these terms, as they prepare for this exam for nearly a decade" doesn't change the argument. In a "3 minutes per question, (2x) 3 hour gauntlet"-exam, tactically picking which to skip, is undeniably part of what's being tested. For such an established institution, I'm going to assume, this is intentional. Given the "less than 0.05% succes-rate, even among the target audience of the exam" it is statistically like, this was one, you were better off skipping. My statement was independent, of the specific contents of the question.

@kaushikmohanta8526 6 күн бұрын

You are right. It's a game of rejecting these questions where the answer would take up at least 6 min of your time Rather solve the easier ones first. And if you feel like you can score this one, then only go ahead. For a tough exam like this, the cutoff usually goes low personally, I'm skipping this one!

@StatsJedi 21 күн бұрын

At the pause, the definition of (A,B) is totally unclear. No wonder so few got it correct.

@chuckywang 21 күн бұрын

Exactly! I thought A and B were just two independent subsets of S.

@sonure6127 21 күн бұрын

What is so unclear in the definition?

@TomNimitz 20 күн бұрын

@@sonure6127 The concept of "independent" in the solution is flawed in the solution, where the poster has applied some twisted logic that actually applies a dependency between A and B that excludes certain otherwise-independent (A, B) combinations separate from the explicit 1

@sonure6127 20 күн бұрын

@@TomNimitz Events X and Y are independent means that P(X intersection Y) =P(X)P(Y) . I hope u get it now.

@sakumar 20 күн бұрын

An event is defined as a subset of the sample space. So, for example, you could say, "If I toss the dice, what is the chances it comes out

@AdrianColley 21 күн бұрын

I would have skipped this question because its phenomenal vagueness is not worth spending exam time on decoding. A must be a set, because |A| is defined only on sets, but it's also an "event associated with S"; which can't indicate the natural meaning of an element of S, because A's cardinality is greater than 1. Whoever wrote that question should have had their work reviewed before it went to print.

@chanlaoshi8634 9 күн бұрын

An event is defined to be a set in probability theory, so the formulation is ok for people who know this term. But when writing a text I would not expect every student to know that and be a bit more clear.

@harshuldesai8901 8 күн бұрын

Well the kids here (India) learn that an event is a subset of the sample space. I honestly didn't understand what the confusion was about but maybe I'm starting to realize the definitions taught aren't the same everywhere. But I do believe this question made sense for most test takers.

@AdrianColley 8 күн бұрын

@@harshuldesai8901 I think you've nailed it here. I was taught probability theory at both second and third level in Ireland, and I never heard that term "event" used with that meaning.

@pablocopello3592 21 күн бұрын

A mathematical problem begins when it is clear what is being asked. Before that, we have a linguistic/notation/convention problem like in this case. Does JEE tests evaluate the knowledge/capacity in it's target topics, or evaluate the capacity to guess what it's questions pretend to ask?

@astrogersunited5389 20 күн бұрын

the competition is high hence such questions are asked

@ParitoshTripathiOfficial 19 күн бұрын

The director of exam board himself said we conduct this exam to eliminate students and not select them. They have to remove students by hook or crook. So, they resort to such techniques by making question ambiguous, incorrect, having multiple correct answers. That is why JEE have the reputation of toughest because no one can guess all questions correctly.

@ParitoshTripathiOfficial 19 күн бұрын

The irony!

@Prabhu108. 15 күн бұрын

Very interesting point. Even a smart person would be troubled if they aren't familiar with the wording.

@chair7728 7 күн бұрын

Obviously math is taught differently around the world but when I read the question I found the wording to be very mathematically exact and completely unambiguous, with the terms having a strict mathematical definition

@sergniko 21 күн бұрын

I paused video to understand the question

@strangelyrepulsive77 21 күн бұрын

i paused to video to wonder at that i will never even understand it

@arthatiara4091 20 күн бұрын

what im thinking when presh said there were only 78 students, "did they have enough time to finish other questions???"😂

@OrbitTheSun 19 күн бұрын

Maybe they just got lucky with their guess. Can someone calculate the probability?

@howareyou4400 18 күн бұрын

This took me about 2 and half minutes to solve. But I took probability class in undergraduate study. I wouldn't be able to understand the concept of "event" there back in high school as it wasn't taught.

@afzal_amanullah 16 күн бұрын

@@howareyou4400What do you mean by you wouldn't understand the concept of Event in your highschool Isn't probability taught in highschool?

@howareyou4400 16 күн бұрын

@@afzal_amanullahBasic probability, yes. But the concept of "event", the one that utilizes the set theory isn't taught until university. You can see that many people in the comment section complain that the "problem description isn't clear". That's likely because their probability class didn't taught the "event" as in the set theory.

@afzal_amanullah 14 күн бұрын

@@howareyou4400 what country are you in?

@aliso-pv7ll 21 күн бұрын

“Oh is a letter, zero is a number!”

@vincent412l7 20 күн бұрын

Nought is a number

@HikingEngineer 21 күн бұрын

yeah this question is bogus -- and i have a math degree -- i'm assuming everyone put 15 as the answer?

@bobh6728 20 күн бұрын

I vaguely remember this from Probability and Statistics class years ago. For example, using dice the sample space S is {1,2,3,4,5,6}. Then you roll the dice (die) once and get a result. That is the experiment. They you can enumerated all the events. An event would be like rolling an even number (2,4,6), or rolling a prime (2,3,5,7). All the events would be the power set of S. Null set (1), (2), (3), etc (1,2), (1,3), etc until you have all subsets. So the wording is standard for sample space, events, independent events, and cardinality.

@robertlezama1958 18 күн бұрын

Agreed. How does an event become a set of elements? The dice reference in the explanation seems to establish that the displayed value is independent of the other 5 possible outcomes, without using probability. Ordered pairs of events where the value of 'A' must always be > that of 'B' led me to 15 for the answer. Or maybe I should be back in math classes. 😢

@bobh6728 17 күн бұрын

@@robertlezama1958 The events are sets of elements. Use rolling a die. There are six possible outcomes for the experiment. But there are 64 events that can be described which are the power set. For example, one event would be throwing an odd number {1,3,5,7} or an even number {2,4,6,8} or less than 4 {1,2,3}. There are 64 different events, which are all the subsets of {1,2,3,4,5,6}. Many are difficult to describe is words like {1,3,4,6}, but it is an event.

@asdfasdfasdf1218 15 күн бұрын

@@robertlezama1958 An event is *defined* as any subset of the sample space. If you don't know the formal definitions of all the terms, then obviously the problem is hard.

@lefthanded3512 21 күн бұрын

You find the true smart folks by asking hard questions in an easy format rather than by asking easy questions in a hard format 👍🏻

@Kounomura 20 күн бұрын

I don't quite agree with that. Because it is also a valuable skill that someone can peel out of the confusion what it is actually about.

@lefthanded3512 20 күн бұрын

@@Kounomura I can agree with that to an extent. It depends what you’re looking for, a linguist, a problem solver, or both.

@prometheus7387 19 күн бұрын

@@Kounomura that's for the English exam to test IMO, not the Math exam

@thechessplayer8328 19 күн бұрын

It seems to me that in science, one tries to explain something that no one understands in a way that everyone can understand, and in poetry, it's the exact opposite.

@fun-damentals6354 20 күн бұрын

i feel like the problem itself is actually rather simple. its the fancy mathematical terms and confusing wording that makes it difficult to understand

@asdfasdfasdf1218 15 күн бұрын

The terms themselves aren't exactly fancy, it's just that they are the strict and formal definitions that nobody uses in everyday speech.

@ravirajshelar250 21 күн бұрын

The 2019 paper is always going to be on the top 5 hardest papers in JEE Advanced History😂. Also in jee advanced papers students generally leave questions related to permuations and combinations a lot as compared to other topics.

@GaurangAgrawal2 21 күн бұрын

I started watching your channel in 8th grade and I was always amazed by how you solved JEE Problems. Especially the ones involving logarithms. Ofc, I wasn't able to understand anything at that time, but now that I am preparing for JEE, It's time to correctly solve this problem in order to check my preparation 😅. Loved these years with you and your way teaching mathematical concepts. Looking for more in the future Edit: Nah This question was from my least favourite topic Permutations, Combination and Probability... I am currently re-studying those topics to understand them better.

@deadlock7946 21 күн бұрын

I wish you the best! Never stop solving and enjoy the process❤

@egaLwie. 21 күн бұрын

wish you best of luck

@makokx7063 20 күн бұрын

Imagine getting through that whole thing then messing up the final addition. lol

@JEE-oq1me 20 күн бұрын

thank you, this is just what i wanted to see 12 days before giving JEE Advanced myself....

@Kshitij.with.nature-channel 20 күн бұрын

😂😂😂

@hamburgeryumyum7491 5 күн бұрын

How did it go?

@JEEsiast 4 күн бұрын

Bro what was ur mains percentile???? Btw how did ur advanced go? mine was good😌

@muthiah9705 20 күн бұрын

I am an Indian student and preparing for this one . Wish good luck for me.

@brahmbandyopadhyay 20 күн бұрын

Good luck ~ from WB

@melanieelayaperuma3110 18 күн бұрын

Google luck, tell us your results!

@lefthanded3512 16 күн бұрын

Good luck man 💯 you got this

@draconic104 15 күн бұрын

@@brahmbandyopadhyay me too........i am a future aspirant

@KrishnaThakur-nf4rt 6 күн бұрын

How was ur advanced?

@dhananjaysawant4646 21 күн бұрын

1:14 for a second I thought that was the math problem

@GWF_YOU 20 күн бұрын

🤦

@yippee8570 20 күн бұрын

It'd be a nice, easy question if it were!

@davidmagdalena8149 18 күн бұрын

🤣🤣🤣🤣🤣🤣🤣🤣

@Vishal00567 12 күн бұрын

I also thought same.

@Kounomura 20 күн бұрын

The strict mathematical language can be so abstract, even in the formulation of the simplest problems, that it directly scares off those who want to get to know the beauties of mathematics. Above all, in education, much more care should be taken to make every mathematical problem as close as possible to an imaginable situation. Once the listeners have understood the essence of the matter through this, it is then possible to continue with the more abstract and generalized version. In the case of the above test, it is not possible to know exactly who they wanted to select in the first place. Those who switch quickly or who have a large overview, even if it is not that deep.

@henryboyter3670 21 күн бұрын

It makes you wonder if the problem had appeared elsewhere and those 78 had read the answer and remembered.

@HikingEngineer 21 күн бұрын

agreed

@BuddyReiner 21 күн бұрын

Nah, each year JEE advanced questions are made totally new, with rare exceptions they give modified and simplified IMO problems sometimes.

@MoonGlow22 21 күн бұрын

I tried to solve in a diffrent way and find the answer 1523 I guess I didnt considered that they have to be independent and did the 10:30 calculation for 6 times İf |A|= 2 3 4 5 6 Then --------------- |B|=1 2 3 4 5 1 2 3 4 1 2 3 1 2 1 Then we calculate Combinations for each one which leads to 15 20 15 6 1 ------------------------ 6 15 20 15 6 6 15 20 15 6 15 20 6 15 6 İf we sum all possible B values for each column we get 6 21 41 56 62 Then 15x6+20x21+15x41+6x56+1x62 = 1523

@MoonGlow22 21 күн бұрын

Also its 23:21 now and I have a electromagnetic wave theory exam tomorrow 😅

@SLuce222 20 күн бұрын

I got the same answer (1523) different method.

@samarthpawar1504 19 күн бұрын

i got the same answer...and i directly skipped to the end to see if i am right and then comes disappointment😮‍💨

@leogreaves3251 21 күн бұрын

It’s always a treat when I get an upload notification from you.

@tan_k 18 күн бұрын

I think the majority of people who solved this question failed the test.

@prabaln4752 9 күн бұрын

😂😂lol

@pranshukumar7934 9 күн бұрын

Or Topped the test.

@prabaln4752 8 күн бұрын

@@pranshukumar7934 that's not the case

@armankumarsingh3566 Күн бұрын

Yes😅

@Gyan-fx9zx 20 күн бұрын

Thanks for making this video on my suggestion.

@aayushprasad7318 14 күн бұрын

Our Jee advanced 2024 exam after 7 days. Wishing all the best to all jee adv 2024 aspirant !

@megabot49 21 күн бұрын

Thats legendary man

@WRSomsky 21 күн бұрын

So where do you get that "A is an event associated with a sample space S" means that A is a *set* of elements drawn from S? I have never heard this before. Without some prior indication of this interpretation, I would take it to mean that A is *an* element drawn from S.

@superman00001 20 күн бұрын

I agree. I thought hard about the meaning of this question and have not yet looked at the solution, but it seems to me there is no justification for interpreting “an event” to mean “the choice of a subset of elements” as opposed to “the choice of an element.” If we use the latter definition, the answer to the question is obviously zero. But why not arbitrarily interpret “an event” as meaning something else - such as a selection of three elements whose product is more than 6, for example? The question wording is unnecessarily and infuriatingly vague.

@sakumar 17 күн бұрын

In probability theory the definition of an event is "subset of the sample space." You could define an event as, say, "the number comes up even." It's the same as saying "the number comes up {2, 4, or 6}. So, event "odd" is {1, 3, 5}. Event "less than 5" is {1, 2, 3, 4}. Event "not 6" is {1, 2, 3, 4, 5} and event "prime" is {2, 3, 5} and so on. In this way, any subset of {1, 2, 3, 4, 5, 6} is an "event."

@asdfasdfasdf1218 15 күн бұрын

That's just definition of "event" in probability. Probability theory uses words in ways that are very different from ordinary usage.

@eliasriedelgarding9949 10 күн бұрын

"Sample space" is the set of possible "worlds" that might come to be. An "event" is something that in each world either happens or not. So you can define it as the set of worlds in which it does happen (i.e. a Boolean function on sample space).

@anishgain2563 21 күн бұрын

From the title i knew it was gonna be a question from jee advanced

@_Dearex_ 13 күн бұрын

even after the explanation i have no idea what this questions wants from me

@OceanusHelios 20 күн бұрын

This problem is difficult not because of the arithmatic involved. This problem is difficult because it is requires knowledge and familiarity of a subset of mathematics that is rarely called into use, and so the level of familiarity with it will be very low. Performance will therefore be based more on how exhaustive a person's education in math is with regards to the landscape of maths overall, than the counter-intuitiveness or complexity of the problem. In other words, if a person was used to solving this type of problem and answering these kinds of questions, it would have been a no-brainer. Just as with the rest of Chemistry and Physics included in this test, it will be a test of the thoroughness of the person's education and a familiarity with the material. It isn't a test of intelligence or anything of the like but a test of skill and how comprehensive the person's knowledge is. In giving a test with these kinds of problems, they could extend the time of the exam to three weeks and would students would still have roughly the same scores. If the exam is meant to weed out and select for the "best of the best" then it is a good test to find your super-nerd in the bunch of test takers.

@chiragmidha2878 4 күн бұрын

I am glad that the Jee exam is recognized as one of the touhgest exams in the world. I gave the test in 2017 and because of that I am still able to follow these math videos, even though I haven't studied math in a while now. Also regarding the percentage of people who got the correct answer. Population of India is huge so a big majority of test takers don't really prepare to that level, however to even give the Jee advance test, you have to get more than certain rank in Jee Mains (an easier version test, (you only have 2 minutes per question in this exam but the questions are easier)). The point that I am trying to make is people who even attempt the Jee advance test have already gotten really scores in the main test.

@cpsof 20 күн бұрын

Sample space means a set of possible outcomes where the outcomes are mutually exclusive, so the cardinality of A and B is always 1, which means that the number of ordered pairs (A, B) where |B| < |A|, is zero.

@NaniNani-yy3sn 10 күн бұрын

This is exactly why i didn't choose to take JEE after 10th 🤯😂

@navghtivs 21 күн бұрын

I think the hard part is to understand the wording, once that's understood, I'd just write a python program to enumerate all combinations and get the answer in no time.

@asdfasdfasdf1218 15 күн бұрын

Probability theory has a knack for formally defining many terms that are different from ordinary usage in English.

@verkuilb 21 күн бұрын

@9:35, you say that with |A| = 3, the only way to get a multiple of 6 is if |B| = 2. Not true-you can also get a multiple of 6 if |B| = 4. I realize that this would violate the rule that |B| < |A|, which I suspect is why you skipped it, but I believe you forgot to state that.

@mk2k685 21 күн бұрын

paused right there and skimmed the comments, thanks for clarifying this

@musicmaker99 20 күн бұрын

I don't understand the question, i don't understand the answer, and i don't understand the explanation. 422 what? How does this relate to dice-throwing?

@drelijahmikail3916 20 күн бұрын

A \intersect B can be 0, e.g. B = {1}, A = {2,3,4,5,6}, which satisfy 1

@Player_is_I 9 күн бұрын

Hats off to "THE 78"

@Vienticus 21 күн бұрын

I got immediately thrown off by the extra comma at the end.

@Indian_Ravioli 13 күн бұрын

i somehow could keep up with your explanation. but why didn't we use the same method as 4&3 or 3&2 for the first case of 6&1..that 62 made sense but cant it be achieved by the same method we got 180 in the other 2 cases?

@deborahd.7281 20 күн бұрын

It took about 13 minutes in the video to solve it and the students had on average 3 minutes to solve it.

@randomguy4803 18 күн бұрын

😂

@olerask2457 9 күн бұрын

I guessed 1523. I read the sample space as rolling a dice, and the independent events as rolling TWO dice. I then had to calculate the sum of all products of binomial coefficients (6,a)*(6,b) under the condition 1

@hhhhhh0175 21 күн бұрын

this question doesn't make any sense unless S is supposed to be the power set of {1,...6}.. how is the "probability" of a subset equal to its number of elements divided by the number of possible elements? that's stated nowhere in the question

@deepvaghasiya3597 21 күн бұрын

Are you a JEE student? Because they don't teach the proper definition of probability, they just say 'favourable outcomes / total outcomes' So, here's the actual definition of probability (discrete probability to be exact) probability is a function P : S -> [0,1], where S is the sample space, and for discrete sample spaces let P_w denote the elementary probability of element w in S, which is 1/|S| here as all are equally likely (probability of any single element), then probability of an event, which is a subset of the sample space, say A, is given by P(A) = Summation(P_w) for all w in A, hence, it will be |A|/|S|.

@kilimanjarocruz660 21 күн бұрын

I totally agree. This is ill-defined in this way.

@jonathanlerner2797 20 күн бұрын

This is exactly what threw me off. The proper probability of any particular subset of S is (1/2)^|S|.

@hhhhhh0175 20 күн бұрын

@@deepvaghasiya3597 i've never seen that definition before. is it supposed to correspond to normal probability for single element sets, and then "extend" it for any subset of the space? is this a well known thing in the context of the exam? and what does it have to do with probability? it seems like a pretty arbitrary definition to me, but i don't live in india, so maybe i'm missing something

@lefthanded3512 20 күн бұрын

They probably assume you will deduce that yourself. If there’s a logical way to do that, then I can see them testing you that way.

@bhanuchhabra7634 21 күн бұрын

Sometimes I am amazed at how easy it is to follow when you explain, but my mind goes blank if I am left with some of the problems. At times I feel writing a program would be faster for me to solve such problems 😅. BTW, i attempted JEE in 2007.

@marutanray 20 күн бұрын

The word event is not defined in the question. Event of sampling from S? Event of what?

@varunsoni5278 2 күн бұрын

Whoever is struggling to understand the question should revisit how an event is defined mathematically

@ramunasstulga8264 21 күн бұрын

Jee aspirants never fail overcomplicate high school problems 🙊

@akshatamritraj7399 16 күн бұрын

Jee is an exam for high school students though

@thekraken4265 13 күн бұрын

Currently a university student and my issue with the computer science, math and statistics courses I’ve taken is that the person making the questions doesn’t clarify things because I assume they think it’s trivial when it’s not.

@bobtoad8601 7 күн бұрын

The difficulty is how badly the question is written.

@NaHBrO733 20 күн бұрын

The hardest part in this question is figuring out what is A and B. If you have a fundamental understanding of mathematical "events", you would know it is a subset of sample space. Then you have to know what is independent, and not confusing it with mutually exclusive. "A,B are subsets of S={1,2,3,4,5,6}, 1

@NaHBrO733 20 күн бұрын

X is a random variable with sample space S. An event A is a subset of S. The probability of "A happening" is the probability of "the instance of X belongs in A"

@sundareshvenugopal6575 15 күн бұрын

Assuming two events are independent iff the outcome of one does not affect or influence the outcome of the other, that means if any two events share the same outcome it cannot be that they are unrelated and independent. The question now becomes, in how many ways can 6 elements of a set be split into two subsets such that one set has more elements than the other, taking into account symmetry of the two sets ?

@user-bg2ct4dy5k 21 күн бұрын

You failed be cause you took 15 minutes to solve a 3 minute problem.

@mr.d8747 21 күн бұрын

*I wanted to say that first:(*

@Schrodinger0 21 күн бұрын

He is explaining the problem, not solving it.

@user-zi6nn2id4m 21 күн бұрын

Mean of 3 minutes not mandate of 3 minutes. Made me laugh though.

@jkid1134 20 күн бұрын

I mean, he also probably just looked it up, which in a test environment would not fly either.

@Maths_3.1415 20 күн бұрын

@@Schrodinger0 These guys just want to show off that they're something special.

@abhinavtripathi692 6 күн бұрын

I appeared for JEE advanced 2024 yesterday!

@ezxd5192 17 күн бұрын

What does "number of ordered pairs (A,B)" means

@Maths_3.1415 20 күн бұрын

It's a standard problem for aspirants of the AMC 12.

@kiranvootori8101 20 күн бұрын

The only reason some could answer correctly is because they don't try to answer every question they get. Part of the test strategy is to find the questions they are strong in and then solve them. Not necessary that they will end up with the correct answer though.

@kapilchhabria1727 13 күн бұрын

I took the IITJEE in 1999 and had a rank of 5000, which is not high enough to secure admission into the program of my choice. When I took it was a 3 hour mathematics and 3 hour physics exam on day 1 and 3 hour chemistry exam on day 2. The exam had two sections, MCQ of which more than one choice could be correct and that was followed by long form questions. Additionally you are not allowed the use of a calculator nor are you permitted to use logarithmic tables. This meant deriving square root using the long form method.

@deepvaghasiya3597 20 күн бұрын

The question is not ill written, it makes sense and it is written perfectly fine. The thing is, the formal definitions are unclear to many people, and so to many students preparing for JEE. In India, students prepare for JEE from coaching institutes, and they usually don't teach formally, they just teach enough to crack the exam, that is they just give mechanical definitions and ideas just to solve normal questions, it is those few students who actually read good books and learn the formal definitions by themselves. Thats the reason this question wasn't solved by many students, whereas it was just the use of basic definitions thats it, the question was lengthy so tough to solve it in given time bound, but conceptually, it was not that tough, just the use of basic definitions.

@chair7728 7 күн бұрын

A lot of people are complaining about the wording being unclear, but the wording is completely unambiguous if you know the mathematical definitions, however I don’t know if the formal definitions are actually taught

@Szynkaa 5 күн бұрын

it's easy and clearly worded (unlike some people in comments suggest), however 3 minutes for this question is incredibly harsh timer

@nedmerrill5705 21 күн бұрын

I need to go to school on this video. I bet it took you longer than 3 minutes on this question...next question, please!

@zecuse 21 күн бұрын

The only thing I got right about this was recognizing it was a combinatorics question.

@powergi3996 21 күн бұрын

The best thing to do on a question like this in an exam is to skip it and use the time on other easier questions, especially if all the questions are worth the same. I'd be very curious to know how much time these 78 people used to answer this.

@Serg_144 2 күн бұрын

Another one "paradox" From the probability theory when you don't write precise enough the definitions... It depends on what the event is in this question There are 2 ways: 1) as in the video, event is {"we choose a subset of S"}. From that perspective the answer is correct. BUT there is another one which for me is more natural (Bernoulli scheme): 2) whe choose a subset from S, but SOME AMOUNT OF TIMES, not one, and also independently, e.g. we have A - subset, and B - subset, we have chosen TWO TIMES a subset from S, independently (!!) by definition. Now the event {A and B} from the 1) perspective is A intersect B. And from the 2) perspective is {"we choose A, and then we choose B"}. Here the answer is 1123 by the way, we simply don't get rid of some terms and summ them all, in comparison to the 1) P.S. kind of not nice to make the students solve the problem with 2 answers, when there is only one.... The problem isn't hard... Its just the fact that the authors didn't thought enough to make a normal task

@iankr 21 күн бұрын

Bleughhhhh. Stats. Didn't understand the wording of the question. Next question.

@prakhar77495 3 күн бұрын

This is not a probability question. Just a PnC question. Some questions are actually poorly worded in jee adv but well when they talk about no of elements it kinda becomes clear that they just want us to make subsets of S. This converts to sum of product of things taken two at a time from C(6,i) where i is from 1-6 you can find it using ((summation x)² - (sum of x²))/2. I guess many people would have messed up the calculations. Many people won't have seen the pattern and would have started calculating the expression without using above formula and then left it bcuz of the heavy calculations.

@tmlen845 21 күн бұрын

does "independent event" have any intuitive meaning in this case?

@lettuce141 21 күн бұрын

It means that that the probability of A is equal to the probability of A given B. In probability theory notation this is P(A) = P(A|B). Intuitively, say you have some x, and probabilities P(A) that x is in A and P(B) that x is in B, then A and B are independent. Let's say I now tell you that x is in A, then this gives you new information that may or may not impact the probability that x is in B. A and B are independent if and only if the information that x is in A does not impact the probability that x is in B. The examples people usually use are coin flips and card draws. If you flip two coins, revealing the result of the first flip doesn't give any information on the second flip. But if you draw two cards from a deck and reveal that the first one is a queen of spades, then you now know that the second card must not be the queen of spades. This changes the probability for the second card from 1/52 for all values to 0 for the queen of spades and 1/51 for all remaining options. Because of this, the two coin flips are independent, and the two card draws are not independent.

@SViyaasJayavel 17 күн бұрын

Cardinal of A U wrote only 5 elements out of 6. Check it

@duryodhan903 6 күн бұрын

I appeared in JEE advanced 2019, and was solving same paper yesterday to know how much can I score now after 5 years. But this question just exhausted me thanks presh to help me out😊😊😊.

@Nepali_guy_Study_yt_account 5 күн бұрын

Did you get admission in IIT bro ???

@OrbitTheSun 19 күн бұрын

Please explain what an event is. If an event is {1,2}, is that two rolls of a die or what? This is pretty unclear to me.

@maxyellen4206 19 күн бұрын

Yeah. And the empty set would be like you haven’t even rolled the dice yet.

@HenrikoMagnifico 21 күн бұрын

Ok how the heck can you do this in 3 minutes

@sparky2141 20 күн бұрын

That's the thing You don't :) You solve the other "easier" questions in less time and invest that saved time into this question Hence the exam also tests your time management skills

@rickyjuwono8000 20 күн бұрын

In my highschool i never learn cardinality

@Tiqerboy 18 күн бұрын

The answer approaches infinity. The problem with this problem is that it doesn't put any bounds on A and B. The set S suggests a six sided die.. I'm interpreting events A and B representing an arbitrary number of rolls of the die. I could roll the die as many times as I want and still have an event A that has as many elements as I want. Therefore if B has just ONE element (i.e. one roll of the die) then there can be an arbitrary number of ordered pairs (A,B) where A is as large as one likes.

@harshuldesai8901 8 күн бұрын

If we assemble a deck of 52 playing cards with no jokers, and draw a single card from the deck, then the sample space is a 52-element set, as each card is a possible outcome. An event, however, is any subset of the sample space, including any singleton set (an elementary event), the empty set (an impossible event, with probability zero) and the sample space itself (a certain event, with probability one). Other events are proper subsets of the sample space that contain multiple elements. So, for example, potential events: "Red and black at the same time without being a joker" (0 elements), "The 5 of Hearts" (1 element), "A King" (4 elements), "A Face card" (12 elements), "A Spade" (13 elements), "A Face card or a red suit" (32 elements), "A card" (52 elements). This is from Wikipedia. Maybe you need to revise your definitions. An event is a subset of the sample space which is S here. Even after an arbitrary number of rolls, the results will always be a subset of S and so the cardinality of both A and B will always be less than or equal to 6.

@MichaelRothwell1 20 күн бұрын

It took me while to get what the question was about, and another while to figure out a reasonable strategy, but in the end my solution was almost identical to the one in the video. 1≤|B|0, |A∩B|>0. If |A|=2, then |B|=1, |A∩B|=1, so 6|A∩B|=6 and |A||B|=2, so 6|A∩B|=|A||B| is false. If |A|=3, then |B|≤2. 2|A∩B|=|B|, so 2 | |B|, so |B|=2, |A∩B|=1. 6C3=20 possibilities for A, 3C1×3C1=3×3=9 possibilities for B in each case, so 20×9=180 possibilities. If |A|=4, then |B|≤3. 3|A∩B|=2|B|, so 3 | |B|, so |B|=3, |A∩B|=2. 6C4=6C2=15 possibilities for A, 4C2×2C1=6×2=12 possibilities for B, so 15×12=180 possibilities. If |A|=5, then |B|≤4, |A∩B|≤4. 6|A∩B|=5|B|, impossible as 5 does not divide into 6 or |A∩B|. If |A|=6, then |A∩B|=|B| (automatically true anyway). 1 possibility for A, B can be any subset of A of size 1 to 5, i.e. 2⁶-2=64-2=62. So 180+180+62=422 possibilities altogether.

@atharvsharma7648 4 күн бұрын

I don't get how are so many people criticizing the language of the question itself. I don't think anything was left unclear, indeed, such questions must be read a few times to digest all the details told in the question. There is nothing wrong with the way the question has been phrased, maybe there are better ways to phrase it, but it's telling all you need to know. An event is simply a subset of sets, thus the first thing that must pop into the mind would be that the only meaningful way to steer ahead would be to take an event as the subset of the provided set and move ahead.

@howareyou4400 18 күн бұрын

It's a normal question in probability class. But that's a undergraduate class...for physics and math major... So this is probably very hard for most high school students. Although I'm disappointed that there is no easier solution and we have to do the calculation with brutal force.

@ExcelInstructor 20 күн бұрын

9:38 How? i mean if A = 3 and we need result being multiple of 6, we have 3 * 2 = 6, but alse 3 * 4 = 12 which is another multiple of 6.

@amanchandra2504 12 күн бұрын

B has to be less than A from the question which says that B is greater than 1 but less than A

@professorpoke 19 сағат бұрын

Presh: "The students get average 3 minutes per question." Also Presh: (Proceeds to make a 15 minute long video."

@nagasaiprajith2302 21 күн бұрын

Nice ❤

@jpopelish 16 күн бұрын

A much easier question: There is a secret, 7 digit integer, made up of one copy of each of the digits, from 2 through 8. What must be added to the 4th digit, to make the secret integer divisible by 9.

@playgirl7305 15 күн бұрын

I assume that the extremely small number of students who got the question 11 just guessed. Because statically, if the majority had guessed, the percentage of correct answers would be higher.

@neutron.o_o 19 күн бұрын

watching this 11days before JEE Advanced

@Vishal00567 12 күн бұрын

good luck bro.

@Chomta 10 күн бұрын

3 days more to go

@absolutezero9874 15 күн бұрын

Good job ignoring 👍🏼👍🏼

@michaeldegrave5905 19 күн бұрын

The GRE being mentioned on the same list as some of these other tests is a laugh.

@mahendraasati5958 13 күн бұрын

They were able to solve the question in the time limit as they had a better way to solve and visualise then you. I was from batch jee 2023 and we were taught that way😅.

@Dhruvalization 10 күн бұрын

Can you solve world hunger? \j

@pawewojtun8335 16 күн бұрын

I finished school with a math test score of 96% and for me this task is completely beyond my understanding. oh

@bilge-nur 20 күн бұрын

Your videos inspire us. I want to continue working for a world where children are not killed or otherwise protected. However, sometimes I have difficulty focusing on my work. My heart aches for what is happening in Gaza. What do you recommend for concentration?

@vcvartak7111 20 күн бұрын

Went overhead

@pranavshankar6222 12 күн бұрын

Is Jee main an AMC12 and Jee advanced an AIME?

@PersonalStash420 20 күн бұрын

Who is Emily Linge? 😀

@aname4731 10 күн бұрын

The wording is kinda confusing but once you understand it it's a neat problem. I got the right answer but it definitely took me more than 3 minutes.

@jeeaspirant6846 19 күн бұрын

The questions asked in JEE ADVANCED are not tough to solve. It’s just how you maintain your composure and stay calm while solving the problem. Once you decode the question and analyse calmly. It can be solved within few minutes.

@gedstrom 17 күн бұрын

I don't even understand what is being asked, so I would have no way of answering the question.🥵

@kiranvootori8101 20 күн бұрын

Just for information. Students appearing for JEE advanced are the top 10% of those who appear in JEE mains.

@varunsoni5278 2 күн бұрын

That's not true. Why are you spreading misinformation?

@TheRMeerkerk 20 күн бұрын

After googling what half these words mean and trying for smaller sample spaces I came to this: There are only going to be independent events for |A|=6 and 1

@TheRMeerkerk 19 күн бұрын

If |A|=4 and |B| =|3|, then P(A)P(B)=1/3. For P(A intersect B)=1/3 to be true, B must have exactly two elements in common with A. There (4 choose 2) ways to choose those elements and (2 choose 1) way to choose the third element which totals to (4 choose 2) x (2 choose 1) = 6 x 2 = 12 possibilities. However, we must not forget that there are (6 choose 4) ways to choose elements for A, which means 12 x (6 choose 4) = 12 x 15 = 180 ways to choose |A|=4 and |B|=3 such that they are independent.

@TheRMeerkerk 19 күн бұрын

If |A|=3 and |B| =|2|, then P(A)P(B)=1/6. For P(A intersect B)=1/6 to be true, B must have exactly one element in common with A. There are (3 choose 1) ways to choose that element and (3 choose 1) ways to choose the other element of B, which totals to (3 choose 1) x (3 choose 1) = 3 x 3 = 9 possibilities to choose B. However, we must not forget that there are (6 choose 3) ways to choose elements for A, which means 9 x (6 choose 3) = 9 x 20 = 180 ways to choose |A|=3 and |B|=2 such that they are independent.

@TheRMeerkerk 19 күн бұрын

If we add all of them together we get a total of 62 + 180 + 180 = 422 pairs (A, B) such that 1

@ygfs8014 21 күн бұрын

I take the Turkish exame called "TYT" which the full name is 'basic sorting test' and this is compared to 2022 TYT hardest question it nearly balanced but never spoken when the HARDEST Questions IN THE WORLD videos

@MoonGlow22 21 күн бұрын

He did a video about a problem from Turkish exam before

@heroadd7320 21 күн бұрын

Can i go into this iits or mit as a marrocan student?

@vedants.vispute77 21 күн бұрын

Yes you can, but you wud need to go to Dubai or directly come to India to give the paper.

@architmishra015 19 күн бұрын

Is your life not going a little too well?

@MagruderSpoots 21 күн бұрын

What purpose was the first sentence?

@chair7728 7 күн бұрын

To tell the test taker that the notation |X| denotes the cardinality of a set X so there is no confusion on the meaning

@pramodsingh7569 21 күн бұрын

Thanks

@ArpitaKumari-hs8cu 10 күн бұрын

You took 15 minutes after knowing the answer( as you must have solved it before making video) . And students are supposed to solve it in just 3 minutes and they see the q for 1st time .😢

@ArpitaKumari-hs8cu 10 күн бұрын

And yes you took 8+ pages while they have to solve in just 1 small page