First things first, this GRE Quant video is about establishing that the 4th quartile [Q4] is good, 1st quartile [Q1] not so good.
A quartile does tell you the proportion of a population that scored below a certain number.
But unless a population is normally distributed, quartiles don’t tell you much more:
Say there is a test scored out of 340.
If I scored a 99th percentile how much more did I score than Person B who scored in the 19th percentile?
What percentage of students scored between my score and Person B’s score? This we can work out. 80%.
Now let’s work out the interquartile Range - useful due to eliminating extremes - of the first 8 multiples of 7.
Q3 [find the median of the last group of numbers, excluding median if necessary] - Q1 [median of first group of numbers]
Box and Whisker diagram explanation, with these numbers:
A) 4, 8, 12
B) 4, 8, 10, 12
C) 4, 5, 7, 9, 10, 11, 11
D) 4, 6, 6, 9, 12
E) 4, 5, 7, 9, 10, 10, 12
A 170 GRE Math extravaganza!
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