The amount of time customers at a “Quick-Change” motor oil store spend waiting f
ID: 3155878 • Letter: T
Question
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 decided to construct a 90% confidence interval (instead of a 95% confidence interval), her margin of error would . . .
be smaller.
be larger.
not change.
become larger or smaller, depending upon the sample taken.
Explanation / Answer
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 decided to construct a 90% confidence interval (instead of a 95% confidence interval), her margin of error would . . .
be smaller.
be larger.
not change.
become larger or smaller, depending upon the sample taken.
CI= mean±t*se or mean±z*se
90% confidence interval is smaller than 95% confidence interval because the table value of t or z at 90% level is smaller than 95% level.
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