The amount of time customers at a “Quick-Change” motor oil store spend waiting
for their cars to be serviced has the Normal distribution with mean μ
and standard deviation σ = 4 minutes. It is company policy that the
customer wait time should be 20 minutes (or less). The manager of a particular
store selects a random sample of 150 customer wait times and observes a mean
wait time of 21 minutes.
A 95% confidence interval for the mean waiting
time for customers is about?