According to internal testing done by the Get-A-Grip tire company, the mean lifetime of tires sold on new cars is 23,000 miles, with a standard deviation of 2,500 miles.
a) If the claim by Get-A-Grip is true, what is the mean of the sampling distribution of 
for samples of size n = 4?
b) If the claim by Get-A-Grip is true, what is the standard deviation of the sampling distribution of 
for samples of size n = 4?
c) If the distribution of tire life is approximately normal, what is the probability that the mean of a random sample of size n = 4 of tire lifetimes will be less than 20,000 miles?
Definitions:
Service Charge
A Service Charge is a fee collected for services provided, often seen in the banking, hospitality, and service industries.
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