Assume the mean useful life of a particular light bulb is 2,000 hours and is normally distributed with a standard deviation of 300 hours. Calculate the useful life of light bulbs within two standard deviations of the mean.

The mean = 2,000

s = Sigma (standard deviation) = 300

M - 2 s = 2,000 - 2 * 300 = 2,000 - 600 = 1,400

M + 2 s = 2,000 + 2 * 300 = 2,000 + 600 = 2,600

Answer.

Useful life of light bulbs within 2 standard deviations of the mean is:

A) Between 1,400 and 2,600 hours