MA 121 Interquartile range help


#1

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.