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A recent study of the lifetimes of smart phones found the average is 24.3 months. Assume...

A recent study of the lifetimes of smart phones found the average is 24.3 months. Assume the population standard deviation is 4.6 months. A simple random sample of 35 smartphones was selected

a) Is it necessary to assume that the lifetimes of smartphones follow a Normal distribution? Briefly explain.

b) What is the probability that the sample mean lifetime would be less than 23 months?

c) What is the probability that the sample mean lifetime would be more than 22 months but less than 26 months?

d) What is the probability that the sample mean lifetime would be more than 26.5 months?

Math   Statistics-And-Probability   
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