statistics
posted by Going crazy .
Please help asap! A tire company is considering a tire replacement company. They have agreed to replace any tire that fails with a life in the bottom 10% of the population. For a given population of tires, the life is a normal distribution with a mean of 27 months and a standard deviation of 3.8 months. What will be the maximum life of a tire to qualify for the replacement program?

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the Z score related to that proportion.
Z = (score  mean)/SD
Substitute the values and solve for the score (months).