# AP Statistics : How to find the quartiles for a set of data

## Example Questions

### Example Question #1 : How To Find The Quartiles For A Set Of Data

Obtain a normal distribution table or calculator for this problem.

Approximate the -percentile on the standard normal distribution.

Explanation:

The -percentile is the value such that  percent of values are less than it.

Using a normal table or calculator (such as R, using the command qnorm(0.9)), we get that the approximate -percentile is about .

### Example Question #1 : How To Find The Quartiles For A Set Of Data

Find the first and third quartile for the set of data

Explanation:

In order to find the first and third quartiles, we haave to find the 25th and 75th percentiles, respectively.

To find the  percentile, we find the product of  and the number of items  in the set.

We then round that number  up if it is not a whole number, and the  term in the set is the  percentile.

For this problem, to find the  and  percentile, we first find that there are 14 items in the set. We find their respective products to be

and

As such, the  and  percentiles are the fourth and eleventh terms in the set, or