Los Angeles workers have an average commute of 33 minutes. Suppose the LA commute time is normally distributed with a standard deviation of 15 minutes. Let X represent the commute time for a randomly selected LA worker. Round all answers to 4 decimal places where possible. a. What is the distribution of X? X N
b. Find the probability that a randomly selected LA worker has a commute that is longer than 38 minutes
c. Find the 80th percentile for the commute time of LA workers. minutes

a) N(33,15).

b) 37.33% probability that a randomly selected LA worker has a commute that is longer than 38 minutes

c) 45.6 minutes.

Step-by-step explanation:

Problems of normally distributed samples are solved using the z-score formula.

In a set with mean and standard deviation , the zscore of a measure X is given by:

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.

In this question, we have that:

a. What is the distribution of X?

Normal with mean 33 and standard deviaton 15. So

N(33,15).

b. Find the probability that a randomly selected LA worker has a commute that is longer than 38 minutes

This is 1 subtracted by the pvalue of Z when X = 38. So

 has a pvalue of 0.6267.

1 - 0.6267 = 0.3733

37.33% probability that a randomly selected LA worker has a commute that is longer than 38 minutes

c. Find the 80th percentile for the commute time of LA workers.

This is X when Z has a pvalue of 0.8. So it is X when Z = 0.84.

45.6 minutes.

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