Question

Quick Start Company makes 12-volt car batteries. After many years of product testing, the company knows that the average life of a Quick Start battery is normally distributed, with a mean of 46.8 months and a standard deviation of 8.1 months. If Quick Start does not want to make refunds for more than 7% of its batteries under the full-refund guarantee policy, for how long should the company guarantee the batteries (to the nearest month)?

In Months?

Answer 1

Given that,

P(Z > 1.48) = 0.07

z = 1.48

Using z-score formula,

x = z * $\sigma$ + $\mu$

x = 1.48 * 8.1 + 46.8 = 59

Answer = 59 months