posted by Stephanie F on .
A new extended-life light bulb has an average service life of 750 hours, with a standard deviation of 50 hours. If the service life of these light bulbs approximates a normal distribution, about what percent of the distribution will be between 600 and 900 hours?
a. 95 percent
` b. 68 percent
c. 34 percent
d. 99.7 percent
e. cannot be determined from the information given.
also please explain how you get the answer...
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 scores.