Exhibit 6-6
The life expectancy of a particular brand of tire is normally distributed with a mean of 40,000 and a standard deviation of 5,000 miles.
-Refer to Exhibit 6-6. What is the probability that a randomly selected tire will have a life of at least 30,000 miles?

Question

Quizplus · Accepted Answer

We need to find the area to the right of 30,000 in a normal distribution with mean=40,000 and standard deviation=5,000. Using the z-score formula, z=(x-μ)/σ, we get z=(30,000-40,000)/5,000=-2. Using a standard normal table or calculator, we find the probability of z being greater than -2 is 0.9772. Therefore, the probability that a randomly selected tire will have a life of at least 30,000 miles is 0.9772 or 97.72%.

Exhibit 6-6 The Life Expectancy of a Particular Brand of Tire Is