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Analyzing Data - Problem 2 1,937 views

Teacher/Instructor Carl Horowitz
Carl Horowitz

University of Michigan
Runs his own tutoring company

Carl taught upper-level math in several schools and currently runs his own tutoring company. He bets that no one can beat his love for intensive outdoor activities!

Using percentiles. Often times, when you get back standardized tests like your ACTs or SATs, you’ll see that you are in the, say 78th percentile or 94th percentile or whatever it may, and what we’re going to do is just briefly talk about how they actually classify that.

So, say we have this string of data listed smallest to largest, and we want to find the number that is in the 80th percentile. What that’s basically referring to is that, there are 80% of the numbers below the number that we’re looking for. All you want to do is, count up the number of piece of information you’re dealing with, in this case we’re dealing with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and so we want to say okay, x out of 10 is equal to 80%. We’re just looking for the 8th term. We can either count forward, or we know this is the 10th, this is the 9th, this is the 8th. So score of 91 would lead you in the 80th percentile.

Similarly for 30th percentile. That is telling us that there are x out of the total number, x out of 10 people below us, so that tells us that we are looking for the third entry. First, second, third, 30th percentile would be score of 78.

When we’re dealing with percentiles, we’re really just looking for the number that fills over the total number, which will give us the percent that we’re looking for.