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 \mu and standard deviation \sigma = 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 99% confidence interval for the population mean wait time based on this sample was calculated to be (20.16, 21.84) minutes.

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 \mu and standard deviation \sigma = 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.

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.

The scores of a certain population on the Wechsler Intelligence Scale for Children (WISC) are thought to be Normally distributed with mean μ and standard deviation σ = 10. A simple random sample of 30 children from this population is taken and each is given the WISC. The mean of the 30 scores is 104.32.

The critical value, z*, used for constructing a 96% confidence interval for population mean \mu is:

[read from the appropriate statistical table in the textbook]

A bottling plant produces one-litre bottles of soda. The actual distribution of volumes of soda dispensed to bottles is Normal, with mean μ and standard deviation σ = 0.05 litre. We randomly select six (6) bottles and measure the volume of soda in each. The results of these six measurements (all in litre units) are

The population of the scores of all high school seniors that took a mathematics test last year followed a Normal distribution, with mean \mu (unknown) and standard deviation \sigma = 100.  A simple random sample of 500 high school seniors that took the same test this year, had a sample mean of 512.

A 95% confidence interval for \mu would be

Crop researchers plant 100 plots with a new variety of corn. The average yield for these plots is

A 99% confidence interval for the average weight μ of a population is computed from a random sample and found to be 4 to 8. We may conclude that

A researcher selects a random sample. A 90% confidence interval for a population mean \mu has