According to a study, 90 % of adult smokers started smoking before 21 years old. 10 smokers 21 years old or older are randomly selected, and the number of smokers who started smoking before 21 is recorded.Find:

1. The probability that at least 3 of them started smoking before 21 years of age.

2. The probability that exactly 3 of them started smoking before 21 years of age.

Guest Oct 13, 2020