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?