The birth control shot is one of most effective methods of birth control available, and it works best when you get the shot regularly, every 12 weeks. Under ideal conditions, only 1% of women getting the shot become pregnant within one year. In typical use, however, 3% become pregnant. Choose at random 20 women using the shot as their method of birth control. We count the number who become pregnant in the next year.
A study of the effectiveness of the birth control shot interviews a random sample of 600 women who are using the shot as their method of birth control.
What is the probability that at least 20 of such women become pregnant in the next year?
A. 0.2389
B. 0.3156
C. 0.6915
D. 0.25