- #1

k77i

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## Homework Statement

The top-selling Red and Voss tire is rated 60000 miles, which means nothing. In fact, the distance the tires can run until wear-out is a normally distributed random variable with a mean of 75000 miles and a standard deviation of 5000 miles.

A. What is the probability that the tire wears out before 60000 miles?

B. What is the probability that a tire lasts more than 85000 miles?

## Homework Equations

z = [X - (mean of X)]/Standard deviation

## The Attempt at a Solution

This is another simple question that I can't seem to be getting correct.

For part A, I did z = (60000 - 75000)/5000 = -3

Then P(z < -3) = 0.0013 according to the chart.. well 0.0013 is P(z= -3.0).. I tried entering the answer for P( z= -2.99) = 0.0014 since it's the last value on the chart lower than -3 also but that was also incorrect.

For part B, z = [85000 - 75000]/5000 = 2

Then P(z > 2) = 1- P(z = 2) = 1 - 0.9772 = 0.0288

Also incorrect..