The owner of a machine shop must decide which of two snack-vending machines to install in his shop. If each machine tested 250 times, the first machine fails to work (neither delivers the snack nor returns the money) 13 times, and the second machine fails to work 7 times, test at the 0.05 level of significance whether the difference between the corresponding sample proportions is significant.

IS IT REASONABLE TO ASSUME THIS SAMPLE CAME FROM A NORMAL POPULATION?

Suppose an instructor would like to know if there is difference in the performance of her two courses of 560 students each. She proceeds to take a random sample of size 50 from each independent class and was able to establish the following results: mean SD Class 1 86 17 Class 2 78 15 Is there a significant difference between the two classes at a significance level of five percent?

A shareholders' group is lodging a protest against your company. The shareholders group claimed that the mean tenure for a chief exective office (CEO) was at least 11 years. A survey of 62 companies reported in The Wall Street Journal found a sample mean tenure of 9.3 years for CEOS with a standard deviation of s = 4.4 years (The Wall Street Journal, January 2, 2007). You don't know the population standard deviation but can assume it is normally distributed. You want to formulate and test a hypothesis that can be used to challenge the validity of the claim made by the group, at a significance level of a = 0.05. Your hypotheses are: H.:µ > 11 На: :и < 11 What is the test statistic for this sample?