perform a one-sample z-test for a population mean using the p value approach. be sure to state the hypothesis and the significance level, to compute the value of the test statistic, to obtain the p value, and to state your conclusion. also assess the strength of the evidence against the null hypothesis.
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, u, of the new light bulbs is larger than last year's mean of 8.5 hours? perform the appropriate hypothesis test using a significance level of 5%. assume that ¤=0.5 hours.