Posted by tara on .
suppose the replacement times for washing machines are normally distributed with mean 8.6 years and standard devistion of 1.6years.
a. what percentage of washing machines have replacement times less than 7 years?
b. find the probability that a washing machine will have a replacement time of more than 6.5 years?

statistics 
PsyDAG,
Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores.