The interquartile range = 9 miles per hour (option C)
Step-by-step explanation:
Rearranging the data set:
1, 2, 2, 3, 4, 5, 5, 7, 9, 10, 12, 13, 19, 20
The total number of data set = N = 14
The median = (N+1)/2
The median = (14+1)/2 = 15/2 = 7.5
The median is the 7.5th position = (5+7)/2 = 12/2 = 6
The median = 6miles per hour
The interquartile range = upper quartile - lower quartile
The interquartile range = Q3 - Q1
Q1 = (N/2 +1)/2 = (14/2 + 1)/2
Q1 = (7+1)/2 = 8/2 = 4
The Q1 is the 4th position (counting is from the front) = 3
Q3 = (N/2 +1)/2 = (14/2 + 1)/2 = (7+1)/2 = 4
The Q3 is the 4th position (counting is from the back) = 12
The interquartile range = 12 - 3 = 9
The interquartile range = 9 miles per hour (option C)