Question

The distribution of speeds along a certain stretch of highway has an mean of 76 mph

and a standard deviation of 7 mph.
What percentage of cars would be traveling slower than 55 mph?

Answer 1

0.13%

Explanation:

Given that :

Mean = 76mph

Standard deviation = 7 mph

Percentage of cars traveling slower than 55mph

Obtain the Zscore :

X = 55mph

Zscore = (X - mean) / standard deviation

Zscore = (55 - 76) / 7

Zscore = - 3

P(Z < - 3)

From the z table :

P(Z < - 3) = 0.0013

Hence, percentage of cars traveling slower than 55mph is (0.0013 * 100%) = 0.13%