here is the question:

A company that manufactures mufflers for cars offers a lifetime warranty on its products provided that ownership of the car does not change. Suppose that only 20% of its mufflers are replaced under this warranty.

a) Define the random variable X as the number of mufflers replaced in a sample of 400 purchases. Give the distribution of X.

b)Referring to part 5a), what is the approximate probability that between 75 and 100 mufflers (inclusive) are replaced under warranty?