6
The data is
8,9,9,10,12,12,13,14,15,15,15,16,18,19,20
There are 15 data points
The median is the 15/2 = 7.5 rounding to 8
The 8th data point
8,9,9,10,12,12,13, 14, 15,15,15,16,18,19,20
Take the 7 points on the left and divide in half
8,9,9, 10 ,12,12,13, 14, 15,15,15, 16, 18,19,2
The interquartile range is the middle of the upper half of the data minus the middle of the lower half of the data
16 - 10 = 6
