Question 4 out of 4.

What is the interquartile range of these numbers?

Z

12

13

14

15

9

10

16

10

8

10

11

12

13

22

23

24

25

The answer is 9. I realize this is a fairly simple topic, but can somebody help me to work out exactly how we get 10 and 19 as our designated 25th and 75th percentiles? I arranged all 18 numbers from 8-25 and tried to group them according to where they should each lie and still can’t quite get the correct answer.