Question

The life of an electric light bulb is known to be normally distributed with a mean of 2000 hours and a std. of 120 hours. Find the probability that the life of such a bulb would be.
(a) greater than 2150 hours
(b) within the range of 1850 hours to 2090 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 proportions/probabilities related to the Z scores.

a. in smaller portion

b. Between Z scores and mean

Answer 2

m;m

Answer 3

0.7768