a.) A fair coin is tossed 15 times. Find the probability that it is heads exactly 8 times.

b.) A coin is weighted so that p(head)=.6. It is tossed 8 times. Find the probability that the number of heads is 5.

c.) A survey found that 26.8% of credit-card-holding families rarely pay off the balance. Find the probability that exactly five families in a survey of twenty credit-card-holding families rarely pay off the balance.