Electric manufactures a decorative Crystal Clear 60-watt light bulb that it advertises will last 1500 hours. Suppose that the lifetimes of the light bulbs are approximately normally distributed, with a mean of 1550 hours and a standard deviation of 57 hours.
(a) What proportion of the light bulbs will last less than the advertised time?
(b) What proportion of the light bulbs will last more than 1650 hours?
(c) What is the probability that a randomly selected GE Crystal Clear 60-watt light bulb will last between 1625 and 1725 hours?
(d) What is the probability that a randomly selected GE Crystal Clear 60-watt light bulb will last longer than 1400 hours?