Read the five problems and determine if you would use a z-interval or a t-interval and why. You do not need to calculate the interval:

Problem

z-interval or t-interval?

Why?

1. A random sample of 16 fluorescent light bulbs has a mean life of 645 hours with a standard deviation of 31 hours. Construct a 95% confidence interval for the population mean, . Assume the population has a normal distribution.

2. A random sample of 56 fluorescent light bulbs has a mean life of 645 hours with apopulationstandard deviation of 31 hours. Construct a 95% confidence interval for the population mean.

3. A random sample of 10 parking meters in a beach community showed the following incomes for a day. Assume the incomes are normally distributed.

$3.60$4.50$2.80$6.30$2.60$5.20$6.75$4.25$8.00$3.00

Find the 95% confidence interval for the true mean.

4. In a recent study of eighth graders on hours of TV watched per week, the number of hours watched is given below:

121015311523123

The population standard deviation is known to be 5.8 hours. Find the 98% confidence interval for the population mean. Assume normality.

5. A local bank needs information concerning the checking account balances of its customers. A random sample of 15 accounts was checked. The mean balance was $686.75 with a standard deviation of $256.20. Find a 98% confidence interval for the true mean. Assume that the account balances are normally distributed.