The top-selling Red and Voss tire is rated 60000 miles, which means nothing. In

Question

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 6000 miles.

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

Probability =

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

Probability = 0.0478 (I got the answer to part B but A is wrong, I tried to get help last night but the person helped me was no help)

Explanation / Answer

A) P(X < 60000) = P( (x - mean)/SD < (60000 - 75000)/6000)

= P(Z < -2.5)

= 0.0062

B) P(x > 85000) = P((x - mean)/SD > (85000 - 75000)/6000

= P(Z > 1.67)

= 1 - P(Z < 1.67)

= 1 - 0.9525 = 0.0475

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