A tire manufacturer designed a new tread pattern for its all-weather tires. Repeated tests were
conducted on cars of approximately the same weight traveling at 70 mph. The tests showed that
the new tread pattern enables the cars to stop completely in an average distance of 120 feet with
a standard deviation of 7 feet and that the stopping distances are approximately normally
distributed.
(a) What is the 80th percentile?
(b) What is the probability that at least 4 out of 10 cars in the study will stop in a distance that is
greater than the distance in part a?
(c) What is the probability that a randomly selected sample of 25 cars in the study will have a
mean stopping distance of at least 130 feet?
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