# 400Practice09 - STAT 400 Lecture BL1 1 Practice Problems 9...

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STAT 400 Lecture BL1 Practice Problems 9 Fall 2014 Dalpiaz 1.Taxes’R’Us Blockis a national chain that prepares income tax returns for individuals. The president of the company wants an average number of 5 customers per clerk per day. On April 15, a random sample of 64 clerks shows the average number of customers per clerk at 4.75. Assume that the overall standard deviation of 1.15. a) Test whether the average number of customers per clerk on April 15 was 5 or it was different. Use α= 0.05. b) Suppose the actual overall average number of customers per clerk on April 15 was 4.8. Was the decision you made in part (a) correct? If not, what type of error has been made?c) What is the p-value of the test in part (a)d) Using the p-value obtained in part (c), would you accept or reject the null hypothesis from part (a) at α= 0.072.In its advertising, Taxes’R’Us Blockclaims that the overall average bill for its services does not exceed \$75. A consumer agency obtains a random sample of 20 tax returns prepared by the company and finds the average preparation bill for those 20 to be \$79.82 with a sample standard deviation of \$10.30. (Assume the amounts of the service fees are normally distributed.) a) We would like to test the claim made in the ad. Perform the appropriate test at a 10% significance level. b) What is the p-value of the test in part (a)c) Was the decision you made in part (a) correct? If not, what type of error has been made? d) Construct a 95% confidence interval for the average bill for services at this firm. ? ? ?