The lightbulbs used to provide exterior lighting for a
Chapter 0, Problem 7.126(choose chapter or problem)
The lightbulbs used to provide exterior lighting for a large office building have an average lifetime of 700 hr. If length of life is approximately normally distributed with a standard deviation of 50 hr, how often should all the bulbs be replaced so that no more than 20% of the bulbs will have already burned out?
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