00:02
We're going to try to figure out if in a random selection of donors, 45 % of them had group o blood, we want to find the probability that at least one out of five donors has group o blood.
00:14
The easiest way to do this, since it says at least one, we don't want to find the probability that one, that two, that three, that four, that five have it and then add them up, because that would be one way to do it.
00:25
The probability one person has group o plus the probability that two people, plus the probability that three, three have it, plus the probability that four have it, plus the probability that five have it, is one way to get the answer.
00:40
But that takes a lot of work.
00:42
We know there's a hundred percent chance that either nobody has it or somebody has group o blood.
00:48
These are called compliments.
00:50
So what we want to do is take that one that represents 100 percent and take away the probability that nobody has it.
00:57
Because the probability that nobody has it and the probability that somebody has it, and the probability has it, which would be all those together, would add up to one.
01:06
So the way we calculate the probability of zero people having group o blood would be the following.
01:12
And i'll do this here in red.
01:14
So this will be the probability that nobody has it...