A city council collected data on driving speeds in order to decide on appropriat

Question

A city council collected data on driving speeds in order to decide on appropriate speed limits. On a major street the mean speed was 38 mph, with a standard deviation of 4.9 mph. On a residential street, speeds had a mean of 23 mph and a standard deviation of 2.7 mph. Relative to the other traffic on that street, which of the following speeds is greater: 42 mph on the major street or 24 mph on the residential street? Show the calculations that justify your answer; round the results to two decimal places.

Explanation / Answer

z score for 42 mph on major street = (42 - 38)/4.9 = 0.81

z score for 24 mph on residential street = (24 - 23)/2.7 = 0.37

Since z score for 42 mph on major street is higher, this speed is greater as compared to 24 mph on residential street.

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