00:01
All right, we're given this identity to prove.
00:03
The probability of a, union, b, given c is equals to the probability of a given c plus the probability of b given c, minus the probability of a intersect b given c.
00:13
For this, we're going to use two of our probability identities, one of which is the multiplication identity, which is as follows.
00:20
The probability of a intersect b, because the probability of a given b times the probability of b.
00:28
And what we're going to do is we're going to rewrite this, it's the probability a given b, so it's the probability of a intersect b over probability of b.
00:44
The second rule we'll need is our addition rule.
00:46
Probability of a union b was the probability of a, plus the probability of b, minus the probability of a intersect b.
01:00
All right.
01:01
So let's use this modified multiplication rule on the left -hand side.
01:05
Of this identity.
01:07
Probability of a, union b, given c equals probability of a, union b, intersects c, all over the probability of c.
01:23
Intersection quote unquote distributes.
01:25
So this becomes probability of a intersect c, union b intersect c, all over probability of c...