The IQR is the difference between Q3 and Q1.
First we need to get the data from the stem and leaf plot:
10, 23, 23, 28,] [33, 45, 80, 90
Since there are 8 data items Q1 would be the median of the lower half (4 items), both are 23 so Q1 is 23.
Q3 is the median of the upper half, since the middle numbers are not the same we need to average 45 and 80. (45 + 80)/2 = 62.5 so Q3 = 62.5
IQR = 62.5 - 23 = 39.5
