Posted by Jacob on .
. A certain company makes 12volt car batteries. After many years of product testing, the company knows that the average life of a battery is normally distributed, with a mean of 45 months and a standard deviation of 7 months. If the company does not want to make refunds for more than 10% of its batteries under the fullrefund guarantee policy, for how long should the company guarantee the batteries (to the nearest month)? my answer was 36m is this correct
58 months
53 months
36 months
45 months
49 months

Statistics 
PsyDAG,
Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the Z score = to that proportion. Put values in the above equation and solve for the score.
It doesn't match your choice.