SOLUTION: The maintenance department of a city�s electric power company finds that it is cost-efficient to replace all street-light bulbs at once, rather than to replace the bulbs individua

Question 835613: The maintenance department of a city�s electric power company finds that it is cost-efficient
to replace all street-light bulbs at once, rather than to replace the bulbs individually as they
burn out. Assume that the lifetime of a bulb is normally distributed, with a mean of 3000
hours and a standard deviation of 200 hours. If the department wants no more than 1% of
the bulbs to burn out before they are replaced, after how many hours should all of the bulbs
be replaced?

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
The maintenance department of a city�s electric power company finds that it is cost-efficient
to replace all street-light bulbs at once, rather than to replace the bulbs individually as they
burn out. Assume that the lifetime of a bulb is normally distributed, with a mean of 3000
hours and a standard deviation of 200 hours. If the department wants no more than 1% of
the bulbs to burn out before they are replaced, after how many hours should all of the bulbs
be replaced?
-----
Find the z-value with a left tail of 1%:
invNorm(0.01) = -2.3263
---
Find the corresponding raw score::
x = z*s + u
x = -2.3263*200+3000 = 2534.73 hrs
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Cheers,
Stan H.
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