An engineer wants to know if the average amount of energy used in his factory per day has changed since last year. The factory used an average of 2,000 megawatt hours (mwh) per day prior to last year. Since last year, the engineer surveyed 400 days and found the average energy use was 2,040 mwh per day. Assume that the population standard deviation is 425 mwh per day. a. Specify the null and alternative hypotheses to determine whether the factory's energy use has changed.
b. Calculate the value of the test statistic and the p-value.
c. At the 5% significance level, can you conclude that the energy usage has changed? Explain.