Question

A police department used a radar gun to measure the speed of a sample of cars on the highway. Assume that the distribution of speeds is approximately Normal with a mean of 71 mph and a standard deviation of 8 mph. Using this distribution what is the z-score of a 65-mph speed limit?

Answer 1

The z-score of a 65-mph speed limit is -0.75

Explanation:

Here, we want to calculate the z-score

To calculate the z-score, we make use of the z-score formula

Mathematically;

z-score =(x-mean)/SD

from the question we identify the values as x = 65 mph, mean = 71 mph, Standard deviation(SD) = 8 mph

Plugging these values into the equation above, we have

z-score = (65-71)/8 = -6/8 = -0.75