Question

A particular telephone number is used to receive both voice calls and fax messages. Suppose that 25% of the incoming calls involve fax messages, and consider a sample of 25 incoming calls. What is the probability that:
a) At most 6 of the calls involve a fax message?
b) Exactly 6 of the calls involve a fax message?
c) at least 6 of the calls involve a fax message?
d) more than 6 of the calls involve a fax message?