Question

NeverReady batteries has engineered a newer, longer lasting AAA battery. The company claims this battery has an average life span of 19 hours with a standard deviation of 0.7 hours. Your statistics class questions this claim. As a class, you randomly select 30 batteries and find that the sample mean life span is 18.6 hours. If the process is working properly, what is the probability of getting a random sample of 30 batteries in which the sample mean lifetime is 18.6 hours or less? Is the company's claim reasonable? (Round your probability to four decimal places.)

Answer 1

µ = 19

sd = 0.7

n = 30

                            

                             = P(Z > -3.13)

                             = 1 - P(Z < -3.13)

                             = 1 - 0.0009

                             = 0.9991