a manufacturer wants to increase the life of her product through a change in the inachining process. prior to the change in the process, a random sample of 100 items showed a mean life of 600 hours with a standard deviation of 40 hours. After the change, another random sample of 100 revealed a mean life of 612 hours with a standard deviation of 30 hours. At the .05 level, has there been a significant increase in product life?