A company that manufactures mufflers for cars offers a lifetime warranty on its products, provided that ownership of the car does not change. Only 20% of its mufflers are replaced under this warranty.
a. In a random sample of 400 purchases, what is the approximate probability that between 75 and 100 (inclusive) mufflers are replaced under warranty?
b. Among 400 randomly selected purchases, what is the probability that at most 70 mufflers are replaced under warranty?
c. If you were told that fewer than 50 among 400 randomly selected purchases were replaced under warranty, would you question the 20% figure? Explain.