The data set we have is:
This data set is already in order from least to greatest, so we don't need to move the order.
Step 1. Find the median of the data set.
The median will be the value at the center of the numbers:
Step 2. Now, we take the two groups at the left and right of the median, marked in green and blue:
And also calculate their median.
For the green set, the median is 10.
And for the blue set, the median is 20.
Step 3. Calculate the interquartile range (IQR) by finding the difference between those two medians (the blue and the green one):
The IQR is 10.
Answer: 10