00:01
Okay, suppose i'm given these probabilities, these given probabilities, and i want to find the probability that b happens, given a happens.
00:07
We'll recall from my last section of conditional probability, this is the probability that a and b happen, given that the probability that a happens.
00:16
What i have here is, first i have the probability b, and then i also have b prime.
00:20
So in my two tree diagrams, i'll have b and then b prime.
00:25
Probability that b happens is 0 .2.
00:28
B prime, the complement of b, 1 minus 0 .2 .2.
00:31
Exactly 0 .8.
00:33
Then i have a and a prime from here.
00:38
So the probability that a happens, given b is 0 .8.
00:44
So then the probability that a prime happens, given b, 1 minus 0 .8 is 0 .2.
00:52
So therefore, the probability that a and b happen, probability b times the probability of a, that's approximately 0 .16, okay? then i need to find the probability that a happens.
01:11
Well, b prime, i'm given a and a prime...