2. 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. This is normally distributed with population standard deviation is

80. [5x2=10]

a. Test the manufacturer's claim at the 0.05 significance level.

b. How your conclusion will be changed if significance level is 1%.