A manufacturer of light bulbs produces 100 Watt(W) bulbs that have lifetimes, L
hours, which are normally distributed with mean 1200 hours and standard deviation
50 hours. What is the probability that a randomly selected 100W bulb has a lifetime,
(a) Less than 1130 hours. (2)
(b) Between 1175 and 1275 hours? (2)
A room is fitted with three new 100W bulbs.
(c) What is the probability that I do not need to replace a bulb in the next 1130 hours?
(3)
In all points we need to use the cumulative distribution function (CDF) of the standard normal distribution, usually denoted with the capital Greek letter .
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