1. The manager at lightbulb factory wants to find out whether there is any difference in mean life expectancy of bulbs manufactured on two different kinds of machines. The population standard deviation of machine I is 100 hours and of machine II is 115 hours. A random sample of 30 lightbulbs from the machine I points out a sample mean of 375 hours, and the similar sample of 30 from machine II points out a sample mean of 362 hours. At a 5% level of significance, is there evidence of difference in the mean fife of bulbs produced by the 2 kinds of machines. What is your conclusion?