posted by Joe .
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?
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.