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
The Out Campaign: Scarlet Letter of Atheism
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 



 

 

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