Posted by victoria on .
A used car dealership has found that the length of time before a major repair is required on the cars it sells is normally distributed with a mean of 10 months and a standard deviation of 3 months. If the dealer wants only 5 percent of the cars to fail before the end of the guarantee period for how many months should the cars be guaranteed?

statistics 
MathGuru,
You will need to find the zscore using a ztable. Remember the question is asking that the dealer wants only 5% of the cars to fail. Keep that in mind when looking for the zscore.
z = (x  mean)/sd >zscore formula
Substitute the zscore you found, the mean, and the standard deviation into the formula, then solve for x.
I'll let you take it from there. 
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K,
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