SOLUTION: Please help with this I am struggling, Research shows the average cell phone will be 26 months before repairs are needed. If the standard deviation for the data is 6 months, wha

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Question 627275: Please help with this I am struggling,
Research shows the average cell phone will be 26 months before repairs are needed. If the standard deviation for the data is 6 months, what length of time should be set for a warranty such that less than 10% of all phones will need repairs during the warranty period.
Thank you
Found 2 solutions by solver91311, ewatrrr:
Answer by solver91311(24713) (Show Source):
You can put this solution on YOUR website!

The Z-score for 10% or less is -1.28. So

Set the warranty period at 18 months.

John

My calculator said it, I believe it, that settles it

Answer by ewatrrr(24785) (Show Source):
You can put this solution on YOUR website!

Hi, Re TY, Yes at less than 26 months... 50% would would be defective...
average cell phone will be 26 months before repairs are needed. If the standard deviation for the data is 6 months
z = (x - 26)/6
what length of time should be set for a warranty such that less than 10% of all phones will need repairs during the warranty period.
= (x-26)/6 | Note: Excel NORMSINV(0.1)= -1.2816
= x