00:01
The american red cross says that about 45 % of the us population has blood type o, 40 % a, 11b, and the rest ab.
00:10
Some volunteers to give blood, what's the probability that the donor has type a, b? well, the sum of probabilities have to add to 1.
00:25
So the probability of ab would be 1 minus the probability of o, a, and b.
00:41
So 1 minus 0 .45 minus 0 .4 minus 0 .11 is 0 .04 or 4%.
00:58
Has type a or b? this we can use the addition rule.
01:09
That's the probability of a, which is 0 .4 plus the probability of b, which is 0 .11.
01:17
And so that would be 0 .51 or 51 % percent.
01:24
That the sum of the probabilities, no, excuse me, is not type o.
01:31
So the probability of not o would be the complement to o, one minus the probability of o, which is 1 minus the probability of o, which is 0, which is 0 0, which is 0 .55.
01:51
Among four potential donors, what's the probability that all of them are type o? well, that would be the probability of all o, which we can use the multiplication rule.
02:13
And so that would be 0 .45 times 0 .45, 4 times for each of the four donors.
02:23
So that's 0 .45 to the 4th or point, we can just call it 0 .01 or 4 .1%...