1. A national car rental company is interested in estimating the difference in mean mileage for SUVs driven in town verses those driven on the highway. They randomly sample 25 SUVs driven only on the highway and 25 SUVs driven only in town. The data from the samples were as follows:

Highway Mileage In-Town Mileage

Average18.6468 16.746

Std dev 4.2969 5.4412

Calculate the 95% confidence interval for the true difference in average mileage (assume equal variances)Interpret your results (in terms of the problem).

2. A marketing company research firm is interested in estimating the difference in the proportion of households in City A who purchase groceries on-line and the proportion of households in City B who purchase groceries on-line. The company randomly samples 150 households from City A and finds 52 who purchase groceries on-line. The company also samples 135 households from City B and finds 60 who purchase groceries on-line.

a) Calculate the 90% confidence interval for the difference in rates. Interpret your results (in terms of the problem).

b) An executive who reads the results of the research claims the results are not valid since the sample sizes were not the same. Comment on that claim.

3. The management at a golf club regularly monitor the golfers on its course for time it takes to finish a round of golf. Suppose a random sample of 36 golfers was taken in 2005 and another random sample of 36 golfers was taken in 2006. The average time in the 2005 sample was 225; the average time in the 2006 sample was 219.

a) Assuming the appropriate test statistic (population mean u5- u6) has a value of 1.68. Is there sufficient evidence to indicate average time has increased in 2006 at the alpha =.05 level of significance? State your conclusion in terms of the problem.