Since the 4 is in the hundredths place in the following numbers, they are all equal. It doesn't matter how many zeros we add, the actual amount of the number will not change. They are all equal amounts: .04 .040 .0400 Even though these numbers are all equal amounts, they have differing amounts of numerals past the decimal. We add more decimal places when we want to be more precise about our measurement. The number of decimal places determine how we would say each number. .04 = 4 hundredths .040 = 40 thousandths .0400 = 400 ten thousandths It really boils down to how precise of a measure you are describing. If its not that precise, I would write it as .04 or say it as "4 hundredths." If I'm talking about a really precise measurement on an important piece of equipment for a satellite, I would write it as .0400 and say it as "400 hundred ten-thousandths." The more decimals we add the more precise the measurement. In your question, the 4 is in the hundredths, but we are looking at the total number of decimal places. In this case there are there are three (tenths, hundreths, THOUSANDTHs) so we use the last decimal place to describe the number.

how would i read in millimeters?