Of the adults in Jefferson county, 10% have had CPR training. For a randomly chosen group of adults from the county, how large would the group have to be in order for the probability that at least one group member has had CPR training to be a least 0.90?
The answer is 22 but I am not sure how to get there exactly. Please help.
The closest I have is:
0.9^n = 0.1
n*ln 0.9 = ln 0.1
n = ln 0.1 / ln 0.9 = 21.85 = 22
Is this the correct way to do this?