1. WestWays magazine sampled random flights from LAX and George Bush Airport (IAH Houston) to compare their rate of delayed departures. For LAX, 255 of the 895 flights sampled were delayed; for IAH, 302 out of 1256. Test at = 0.05 whether these samples indicate a different delayed departure rate for these airports. Do the test by hand (using Minitab just for the p-value) and confirm your results with Minitab. Interpret your results and state your conclusion in terms of the data.

2. Merrill Sachs asked major customers to rank their 2 newest financial consultants. The results are summarized below:

Consultant A: Avg. rating 6.82/7 by 16 customers. Sample std. deviation = 0.64

Consultant B: Avg. rating 6.25/7 by 10 customers. Sample std. deviation = 0.75

a. What assumption(s) must be made for a 2-sample t test of the difference in the ratings to be valid?

b. Making that assumption, conduct a 2-sample t test at = 0.05 of the difference in ratings. Do the test by hand (using Minitab just for the p-value) and confirm your results with Minitab. (The degrees of freedom for this test = 16.) Interpret your results and state your conclusion in the terms of the data.

c. Suppose that, instead of 16 and 10 the sample sizes were 160 and 100, respectively. Repeat the test using Minitab. Interpret your results and state your conclusion in terms of the data.

9. In a contentious shareholder lawsuit, a critical claim by the plaintiffs is that average CEO tenure for companies of at least $2 billion in market cap is 9 years. A survey of 36 such companies had a sample mean of 7.67 with a sample standard deviation of 6.48. Use this sample to test at the 5% level whether the average CEO tenure is less than 9 years. Do the test by hand (using Minitab just for the p-value) and confirm your results with Minitab. Interpret your results and state your conclusion in terms of the data.

10. Assume that we randomly sample 200 residents of Indiana and ask them if they favor having the government issue marriage licenses to same-sex couples. 104 say that the do; 96 dont. Test at the 5% level whether the population support for this proposition is greater than 50%. Do the test by hand (using Minitab just for the p-value) and confirm your results with Minitab. Interpret your results and state your conclusion in terms of the data.

12. Drug clinical trials are analyzed using hypothesis testing methods. As weve discussed, the null hypothesis in the effective stage of such trials is that the drug being tested is ineffective. The alternative, of course, is that the drug is effective. Explain why such tests are usually done with low -levels.