Many women take oral contraceptives to prevent pregnancy. Under ideal conditions,1% of women taking the pill become pregnant with in one year. In typical use, however, 5% become pregnant.
A study of the effectiveness of oral contraceptives interviews a random sample of 20 women who are taking the pill.
Based on the information about typical use, what is the probability that at least 25 of these women become pregnant in the next year? Is the Normal approximation permissible?