Question

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. what is the probability that a randomly selected tire will have a life of at least 30,000 miles?

Answer 1

The z-score of 30,000 is -2. Reference to a normal standard distribution table shows that 97.72% of tires will have a life of at least 30,000 miles.