A tire manufacturer has a 60,000 mile warranty for tread life. The manufacturer considers the overall tire quality to be acceptable if less than 5% are worn out at 60,000 miles. The manufacturer tests 250 tires that have been used for 60,000 miles. They find that 3.6% of them are worn out. With this data, we test the following hypotheses. H0: The proportion of tires that are worn out after 60,000 miles is equal to 0.05. Ha: The proportion of tires that are worn out after 60,000 miles is less than 0.05.

What assumption about the sample underlies the hypothesis test?

a. The sample comes from a population of tires with 60,000 miles where 5% of tires are worn out.

b. The sample comes from a population of tires with 60,000 miles where 3.6% of the tires are worn out.

c. The sample comes from a population of tires where 250 are used for 60,000 miles.

d. The sample comes from a population of 250 tires that have a 60,000 mile warranty.