Question

Speed (mph)

58
72
55
65
70
81
66

Consider the speed in miles per hour that Officer Williams clocked the last seven drivers with his radar. Find the interquartile range of the speeds.
A) 5
B) 7
C) 14
D) 21

Answer 1

C

Explanation:

In this question, we are asked to calculate the interquartile range of the speed values given in the question.

Firstly, we need to order the values of the speed from the lowest to the highest. That would be;

55 58 65 66 70 72 81

Now, we determine the first quartile position which is Q1. That would be (N+1)/2 where N is the number of data points which is 7 according to this question

We have (7 +1)/4= 8/4= 2

The value at the 2nd position counting from left is 58

For the third quartile , Q3, we have 3 * (N+1)/4 = 3 * 2 = 6

The value at the 6th position counting from left is 72

mathematically, the formula for the interquartile range is Q3 - Q1 = 72 - 58 = 14