On the average, a certain computer part lasts  1/4.0  years.

a. What is the probability that exactly 7 computer parts last a year? [Here number of lasting computer parts, is discrete random variable, not a continuous variable

B. What is the probability that at most 3 computer parts last a year?

C. What is the probability that a computer part lasts between 1/8.0 years and 1/4.0 years? [The length of lasting time of the computer part is a continuous random variable]