1. The packaging of a certain light bulb states that the light bulb will last for 8000 hours under normal use. A random sample of 15 light bulbs indicated an average lifetime of 7850 hours with a standard deviation of 500 hours. A costumer suspects that the average life is different from 8000 hours. Is there enough evidence to believe that the average life is not 8000 hours? Use 0.05 level of significance