1. Some IQ scores are standardized with a mean of 100 and a standard deviation of 16. Determine:
a. In what interval you would expect the middle 95% of the IQ scores to be found.
b. What percent of people would have an IQ score above 116.
c. What percent of people would have an IQ score between 68 and 84.
d. What percent of people would have an IQ score of at least 132.
e. What percent of people would have an IQ score of no more than 68.
f. What percent of people would have an IQ score of 100 or above.
2. A tire manufacturer believes that the tread life of its snow tires can be described as a normal distribution with
a mean of 32,000 miles and a standard deviation of 2500 miles.
a. If you buy a set of these tires, would it be reasonable to expect they will last 40,000 miles?
b. What percentage of these tires can be expected to last less than 30,000 miles?
c. What percentage of these tires can be expected to last between 30,000 and 35,000 miles?
d. Estimate the IQR of the tires' tread life.
e. In planning a marketing strategy, a local tire dealer wants to offer a refund to any customer whose tires fail to last a certain number of miles. However, the dealer does not want to take to big a risk.
If the dealer is only willing to give a refund to no more 2% of the customers, for what mileage can he guarantee these tires to last?