Chapter 8.3, Problem 1TY

A shoe manufacturer claims that athletes can decrease their times in the 40-yard dash using the manufacturer’s training shoes. The 40-yard dash times of 12 randomly selected athletes are measured. After the athletes have used the shoes for 8 months, their 40-yard dash times are measured again. The times (in seconds) are listed in the table below. At α = 0.05, is there enough evidence to support the manufacturer’s claim? Assume the times are normally distributed. (Adapted from Coaches Sports Publishing)