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 43.0 months and a standard deviation of 8.9 months. If Quick Start guarantees a full refund on any battery that fails within the 36-month period after purchase, what percentage of its batteries will the company expect to replace?

(Round your answer to two decimal places.)

Answer 1

Solution :

Given that ,

mean = = 43.0 months

standard deviation = = 8.9 months

P(x < 36) = P[(x - ) / < (36 - 43.0) / 8.9 ]

= P(z < -0.79)

Using z table,

= 0.2148

The percentage is = 21.48%