Question

a. Assume that a sample is used to estimate a population proportion p. Find the 95% confidence interval for a sample of size 198 with 42 successes.

Enter your answer as an open-interval (i.e., parentheses) using decimals (not percents) accurate to three decimal places.

95% C.I. =

b. A political candidate has asked you to conduct a poll to determine what percentage of people support her.

If the candidate only wants a 0.5% margin of error at a 99% confidence level, what size of the sample is needed?

Give your answer in whole people.

c. You want to obtain a sample to estimate a population proportion. Based on previous evidence, you believe the population proportion is approximately p*=70%p*=70%. You would like to be 99% confident that you estimate is within 1.5% of the true population proportion. How large of a sample size is required?

n =

d. You want to obtain a sample to estimate a population proportion. At this point in time, you have no reasonable estimate for the population proportion. You would like to be 95% confident that you estimate is within 0.2% of the true population proportion. How large of a sample size is required?

n =

Hint: Shouldn't the answer be a WHOLE NUMBER.

Do not round mid-calculation. However, use a critical value accurate to three decimal places.

Answer 1

(a)

0.155	confidence interval 95.% lower
0.269	confidence interval 95.% upper

(b) 66349

(c) 6193

(d) 240092