Answer: B. 9
Step-by-step explanation:
First, find the median of the data set. This set has an even number of points, so find the average between the two middle points: 18 and 19. 18+19 = 37. 37/2 = 18.5. The median is 18.5.
Now, to find the lower quartile, find the median of the lower half of the data set {11, 12, 14, 15, 18}. The number in the middle is 14. The lower quartile is 14.
To find the upper quartile, find the median of the upper half of the data set {19, 21, 23, 25, 55}. The number in the middle is 23. The upper quartile is 23.
To find the interquartile range, subtract the lower quartile from the upper quartile. 23-14 = 9. The interquartile range is 9.
