question 23

In a survey of 2951 adults, 1483 say they have started paying bills online in the last year.

Construct a99% confidence interval for the population proportion. Interpret the results.

A99% confidence interval for the population proportion is (___, ___)

(Round to three decimal places asneeded.)

question 24

A researcher wishes toestimate, with 95% confidence, the population proportion of adults who think the president of their country can control the price of gasoline. Her estimate must be accurate within 2% of the true proportion.

a) No preliminary estimate is available. Find the minimum sample size needed.

b) Find the minimum sample sizeneeded, using a prior study that found that 36% of the respondents said they think their president can control the price of gasoline.

c) Compare the results from parts(a) and(b).

question 26

Find the critical values 2L and 2R for the given confidence level c and sample size n.

c=0.99, n=23

2L=

(Round to three decimal places asneeded.)

question 27

Use technology to construct the confidence intervals for the population variance 2 and the population standard deviation . Assume the sample is taken from a normally distributed population.

c=0.95, s=32, n=19

The confidence interval for the population variance is (__, __)

(Round to two decimal places asneeded.)

question 28

The number of hours of reserve capacity of 10 randomly selected automotive batteries is shown to the right.

1.75

1.88

1.51

1.67

1.77

1.96

1.39

1.56

1.45

2.09

Assume the sample is taken from a normally distributed population. Construct 90% confidence intervals for(a) the population variance 2 and(b) the population standard deviation .

question 29

A magazine includes a report on the energy costs per year for32-inch liquid crystal display(LCD) televisions. The article states that 14 randomly selected32-inch LCD televisions have a sample standard deviation of $3.71. Assume the sample is taken from a normally distributed population. Construct 90% confidence intervals for(a) the population variance 2 and(b) the population standard deviation . Interpret the results.

question 30

The waiting times(in minutes) of a random sample of 20 people at a bank have a sample standard deviation of 4.8 minutes. Construct a confidence interval for the population variance 2 and the population standard deviation . Use a 99% level of confidence. Assume the sample is from a normally distributed population.

What is the confidence interval for the population variance 2?

(Round to one decimal place asneeded.)