The lifetime of a particular type of light bulb are approximately normally distributed with a mean of 1200 hours and a standard deviation of 140 hours.
a) Find the probability that a randomly chosen bulb will burn longer than 1400 hours.
b) Find the probability that a randomly chosen bulb will last between 1000 and 1050 hours
c) Twenty percent of the lightbulbs have a lifetime of less than what value?
d) At what number of hours should the warranty lifetime be set so that only 2% of bulbs must be replaced under warranty?