Question

Among U.S. cities with a population of more than 250,000 the mean one-way commute
to work is 25 minutes. The longest one-way travel time is New York City, where the
mean time is 40 minutes. Assume the distribution of travel times in New York City
follows the normal probability distribution and the standard deviation is 7.5 minutes.
a. What percent of the New York City commutes are for less than 30 minutes?
b. What percent are between 30 and 35 minutes?

Answer 1

(A) given that

mean = 40

standard deviation = 7.5

we have to find P(X< 30)

using the formula

converting to percent, we get

0.0918*100 = 9.18%

(B)

given that

mean = 40

standard deviation = 7.5

we have to find P(30<X< 35)

using the formula

converting to percent, we get

0.1596*100 = 15.96%