A particular telephone number is used to receive both voice calls and fax messages. Suppose that 30% of the incoming calls involve fax messages, and consider a sample of 20 incoming calls.

a) What is the probability that exactly 5 calls involve fax messages?
b) What is the probability that at least 10 calls involve fax messages?
c) What is the expected number of calls involving fax messages in the sample?
d) What is the standard deviation of the number of calls involving fax messages in the sample?