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?

Question

A) About 25%
B) About 50%
C) About 75%
D) About 68%

Answer 1

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.