question 9

People were polled on how many books they read the previous year. How many subjects are needed to estimate the number of books read the previous year within one book with 90% confidence? Initial survey results indicate that =16.3 books.

A 90% confidence level requires _____ subjects.

(Round up to the nearest whole number asneeded.)

question 10

A doctor wants to estimate the HDL cholesterol of all20- to29-year-old females. How many subjects are needed to estimate the HDL cholesterol within 3 points with 99% confidence assuming =15.8? Suppose the doctor would be content with 95% confidence. How does the decrease in confidence affect the sample sizerequired?

A99% confidence level requires ______ subjects.

(Round up to the nearest whole number asneeded.)

question 11

A soccer ball manufacturer wants to estimate the mean circumference of soccer balls within 0.05 in.

(a) Determine the minimum sample size required to construct a 95% confidence interval for the population mean. Assume the population standard deviation is 0.25 in.

(b) Repeat part(a) using a population standard deviation of 0.35 in. Which standard deviation requires a larger samplesize? Explain.

question 12

A soccer ball manufacturer wants to estimate the mean circumference ofmini-soccer balls within 0.05 inch. Assume the population of circumferences is normally distributed.

(a) Determine the minimum sample size required to construct a 95% confidence interval for the population mean. Assume the population standard deviation is 0.20 inch.

(b) Repeat part(a) using a population standard deviation of 0.30 inch.

(c) Which standard deviation requires a larger samplesize? Explain.

question 14

Find the critical value tc for the confidence level c=0.90 and sample size n=11.

tc=

(Round to the nearest thousandth asneeded.)

question 15

Find the critical value tc for the confidence level c=0.98 and sample size n=12.

tc=

(Round to the nearest thousandth asneeded.)