The mean lifetime of a battery is 60 months, with a standard

[srt927]

The mean lifetime of a battery is 60 months, with a standard deviation of 5 months. the manufacturer is willing to fully refund any battery that fails during the warranty period. What is the maximum length for the warranty period if the manufacturer is willing to fully refund no more than 5% of the batteries?

What formulas are used?

 

[galactus]

Find which z-score corresponds to .05.

Set the formula \(\displaystyle z=\frac{x-{\mu}}{\sigma}\) equal to it and solve for x.

All of these problems you have listed are a variation on a theme. They all implement the z-score formula.

 

[srt927]

Cool thanks