Word Problem

[Rainbow]

Research of a manufacturer of cell phones shows that the average cell phone will be 26 months before there is a need of repairs. If the standard deviation for the data is 6 months, what length of time should the manufacturer set for a warranty such that less than 10% of all cell phones will need repairs during the warranty period?

 

[DrPhil]

Research of a manufacturer of cell phones shows that the average cell phone will be 26 months before there is a need of repairs. If the standard deviation for the data is 6 months, what length of time should the manufacturer set for a warranty such that less than 10% of all cell phones will need repairs during the warranty period?

As a Pre-Algebra question, I am at a loss on what methods you would have to work it. What is needed is a table of the Normal Distribution. Please show what you have done (or tried), so we may know where you need help.