Suppose that the amount of time teenagers spend on the Internet is normally distributed, with a standard deviation of 1.5 hours. A sample of 100 teenagers is selected at random, and the sample mean is computed as 6.5 hours. Determine the 99% confidence interval estimate of the population mean.

Question 1
A survey of 100 retailers revealed that the mean after-tax profit was $80 000. Assuming
that the population standard deviation is $15 000, determine the 95% confidence interval estimate of the mean after-tax profit for all retailers.

Question 2
Suppose that the amount of time teenagers spend on the Internet is normally distributed, with a standard deviation of 1.5 hours. A sample of 100 teenagers is selected at random, and the sample mean is computed as 6.5 hours.

Determine the 99% confidence interval estimate of the population mean.

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