In the United States, the probability of having twins (usually about 1 in 90 births) rises to about 1 in 10 for women who have been taking the fertility drug Clomid. Among a group of 10 pregnant women, what's the probability that
a) at least one will have twins if none were taking a fertility drug?
b) at least one will have twins if all were taking Clomid?
c) at least one will have twins if half were taking Clomid?