A manufacturer claims that the mean lifetime of its lithium batteries is 1400 hours. A homeowner thinks it may be different from 1400 hours. He randomly selects 40 of these batteries and finds the mean lifetime to be 1370 hours with a standard deviation of 80 hours. Test the manufacturer’s claim at the 0.05 significance level.

Question

A manufacturer claims that the mean lifetime of its lithium batteries is 1400 hours. A homeowner thinks it may be different from 1400 hours. He randomly selects 40 of these batteries and finds the mean lifetime to be 1370 hours with a standard deviation of 80 hours. Test the manufacturer’s claim at the 0.05 significance level.

Answer 1

Z = (score-mean)/SD

Z = (1370-1400)/80 = ?

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.