Question

A local civil engineer takes a survey of the traffic at the intersection of Haight Avenue and 8th street for 10 minutes at noon on 5 randomly selected days. The survey predicts that the distribution of traffic is roughly normally (bell-shaped) distribution with the average number of cars per 10 minutes is 6 cars and the standard deviation is 1.5 cars. (a) List below the 1-SD, 2-SD and 3-SD intervals. (b) Using the empirical rule to estimate the percentage of days where there would be over 9 cars per 10 minute period

Answer 1

b.)Over 9 cars, we can see in the above interval it is (3,9), and it is within 2 standard deviation of the mean.

According to the Empirical rule 95% data lie within 2-standard deviation of the mean.

Hence

the percentage of days where there would be over 9 cars per 10 minute period=(100-95)/2=2.5%