I am so confused on how to do this :S
Among U.S. cities with a population of more than 250,000 the mean one-way commute to work is 24.3 minutes. The longest one-way travel time is New York City, where the mean time is 38.3 minutes. Assume the distribution of travel times in New York City follows the normal probability distribution and the standard deviation is 7.5 minutes.
What percent of the New York City commutes are for less than 30 minutes?
What percent are between 30 and 35 minutes?
What percent are between 30 and 40 minutes?
2007-10-24 08:52:34 · 1 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
The probability that the commute is less than 30 minutes is the standard normal value N_Z for (30 - 38.3)/7.5
(30 - 38.3)/7.5 = -1.107 The standard normal tables give 0.1349 (I interpolated between the values of -1.10 and -1.11, which are .1357 and .1335, respectively). So it's about 13.5% of commutes.
For a commute between 30 and 35 minutes, find the N_Z value for (35 - 38.3)/7.5 and then subtract 0.1349
Use a similar calculation to answer the last question.
2007-10-24 10:01:40 · answer #1 · answered by Ron W 7 · 0⤊ 3⤋