Suppose that the certain lifetimes of a certain light bulb are normally distributed with μ=1500 hours and σ=200. Find the probability that a light bulb will burn out in less than 1200 hours.

Answer 1

Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to the Z score.

Answer 2

Z=(X<1.5)=0.4332+0.5=0.9332