Asked by Joan

If light bulbs have lives that are normally distributed with a mean of 2500 hours and a standard deviation of 500 hours, what percentage of light bulbs have a life less than 2500 hours?
A) About 25%
B) About 50%
C) About 75%
D) About 68%

Answers

Answered by Steve
since 2500 is exactly the mean (0 std away), look up

P(Z < 0) in your standard table.

Or, just consider the data and pick what seems reasonable in that case.
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