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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 and standard deviation = 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. If the manager had selected more customers for her sample, the margin of error in the 95% confidence interval would . . .

become larger. not change. become smaller. become larger or smaller, depending upon the sample taken.