20.)(1 point) Example 14.1 (page 352) described NHANES survey data on the body mass index (BMI) of 654 young women. The mean BMI in the sample wasxx= 26.8. We treated these data as an SRS from a Normally distributed population with standard deviation= 7.5.

(a) Give three confidence intervals for the mean BMIin this population, using 90%, 95%, and 99% confidence.

(b) What are the margins of error for 90%, 95%, and 99% confidence? How does increasing the confidence level change the margin of error of a confidence interval when the sample size and population standard deviation remain the same?

(1)90%:to

95%:to

99%:to

(2)90%:

95%:

99%:

21.) (1 point) A medical researcher wants to investigate the amount of time it takes for patients' headache pain to be relieved after taking a new prescription painkiller. She plans to use statistical methods to estimate the mean of the population of relief times. She believes that the population is normally distributed with a standard deviation of 24 minutes. How large a sample should she take to make an estimate within 5 minutes of the mean time with 96% confidence?

Sample Size =