Chapter 7, Problem 7.9TI

Use the information in Example 7.9, but change the sample size to 144.

a. Find $P\left(20<\bar{x}<30\right)$ .

b. Find P( ${\displaystyle \sum x}$ is at least 3,000).

c. Find the 75^th percentile for the sample mean excess time of 144 customers.

d. Find the 85^th percentile for the sum of 144 excess times used by customers.