Instructions:

1) Complete the exam yourself. You may not work with anyone on an exam.

2) Show your work. For calculator problems, record the command(s) you used. Show all parts of each hypothesis test!!!!!!!

3) Do your calculations using formulas unless otherwise indicated.

4) You may assume that all samples are simple random samples.

1. What shape did I draw at the bottom of your graded Assignment 7?

2. What requirements (besides having a simple random sample) must be met to use the z-distribution to test a claim about a proportion?

3. What requirements (besides having a simple random sample) must be met to use the z-distribution to test a claim about a mean?

4. You are studying the mean cost of a emergency room visit. How many visits should you include in your sample to be 95% confident that your sample mean is within $250 of the population mean? Assume that the population standard deviation is known to be $790.

5. You are studying the proportion of emergency room bills that are not paid. How many bills should be in your sample to be 99% confident that your results are within .02 of the actual proportion?

6. The daily number of calls received at a call center is normally distributed. In a sample of 26 days, there was a mean of 521.5 calls with a standard deviation of 51.7 calls.

a. Create a 95% confidence interval estimate for the standard deviation in daily number of calls at the call center. Use formulas and chart.

b. Create a 95% confidence interval estimate for the mean daily number of calls at the call center. Use formulas and chart.

c. If the population standard deviation is known to be 68.6 calls, find a 95% confidence interval estimate for the mean daily number of calls at the call center. Use your calculator, and interpret your results ("We are...).

6. The daily number of calls received at a call center is normally distributed. In a sample of 26 days, there was a mean of 521.5 calls with a standard deviation of 51.7 calls. (Continued.)

d. With .01 significance, test the claim that the standard deviation in daily number of calls is 80. Use the critical value method.

e. With .05 significance, test the claim that the mean daily number of calls is greater than 500. Use the P-value method.

7. In a sample of 42 employers in a city, 64% offered vacation to employees during their first year.

a. Create a 90% confidence interval estimate for the proportion of employers who offer vacation to first-year employees. Use formulas and chart.

b. With .10 significance, test the claim that 55% of employers offer vacation to first-year employees.

Use your calculator.