Question

In practical use, oral contraceptives have a 5% chance of failing. If a doctor has 10 patients using oral contraceptives, what is the probability that at least 1 will get pregnant?

Answer 1

Here's one way to do this problem:

n = 10
p = .05
q = 1 - p = 1 - .05 = .95

You will need to find P(0). You can then take 1 - P(0) for your probability, which is easier than finding P(1) through P(10).

You can use a binomial probability table, or calculate by hand using the following formula:
P(x) = (nCx)(p^x)[q^(n-x)]


I'll let you take it from here.