Confidence Intervals and Hypothesis Testing 1. Identify the following critical values: A. 2 z for a confidence level of 99% B. 2 t for n = 15 and a confidence level of 95% 2. A NAPA Auto Parts supplier wants information about how long car owners plan to keep their cars. A random sample of 41 car owners results in a mean of 7 years with a standard deviation of 3.75 years. Find a 95% confidence interval for the true population mean. Identify the point estimate for mean and margin of error. 3. In a gallop poll of 1000 adults, 930 said that restaurants and bars should refuse service to patrons who had too much to drink. Find a 90% confidence interval for the true percentage of patrons with this view. Identify the point estimate for the percentage and the margin of error. 4. Among those taking the Graduate Record Exam, 18 people are randomly selected. This group had a mean score of 550 and a standard deviation of 140. What is the 95% confidence interval for the population mean for the GRE test. Identify the point estimate for the mean and the margin of error. 5. A USU Today survey found that of the gun owners surveyed 275 favor stricter gun laws. The survey Involved 500 gun owners. Test the claim that a majority (more than 50%) of gun owners favor stricter gun laws. Use a .05 significance level. 6. The Phillies were accused of cheating their beer customers by not putting enough beer in their 12 oz cups. When 15 cups were selected at random, they were found to have a mean of 11.7 ounces with a standard deviation of 0.5 ounces. At the .01 significance level, test the claim that the customers are being cheated. 7. An employer claims that full time employees have a mean income of $35,000. A sample of 200 employees was considered. Their mean salary was $34,000. Assume a population standard deviation of $4,000. Does her claim seem reasonable at a 0.05 level of significance? 8. You want to estimate the percentage of statistics students who get grades of C or better. How many students should you survey to be 95% confident that the sample percentage is off by no more than 2 percentage points. 9. A researcher wants to estimate the mean serum cholesterol level for college age women. In a past study the standard deviation for this measure was 42 units. If the researcher wants to be off in his estimate by no more than three units (with 99% confidence), how large must his sample be?

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