Last year, the mean running time for a certain type of flashlight
battery was 8.5 hours. This year, the manufacturer has introduced a
change in the production method which he hopes will increase the
mean running time. A random sample of 40 of the new light bulbs was
obtained and the mean running time was found to be 8.7 hours. Do
the data provide sufficient evidence to conclude that the mean
running time of the new light bulbs is larger than last year mean
of 8.5 hours? Perform the hypothesis test using a significance
level of 5%. Assume that population standard deviation is 0.5
hours. What is your conclusion?