# Thread: probability of A given B.

1. ## probability of A given B.

HI; Just need to check if this is correct,Whats the probability of A given B?

P(A) = 1/2
P(B) = 1/2
P(A | B) = P(AB) / P(B).
P(AB) = P(A) + P(B) - P(A B).
= 3/6 + 3/6 – 4/6.
= 6/6 - 4/6.
= 2/6 = 1/3.

P(A | B) 1/3 / 3/6 = 1/3 * 6/3 = 6/9.
= 2/3.

Thanks.

2. ## Re: probability of A given B.

Originally Posted by anthonye
HI; Just need to check if this is correct,Whats the probability of A given B?

P(A) = 1/2
P(B) = 1/2
P(A | B) = P(AB) / P(B).
P(AB) = P(A) + P(B) - P(A B).
= 3/6 + 3/6 – 4/6.
If all you were given is that "P(A)= 1/2" and "P(B)= 1/2" (above) where did you get " $P(A\cap B)= 4/6$?

= 6/6 - 4/6. = 2/6 = 1/3.

P(A | B) 1/3 / 3/6 = 1/3 * 6/3 = 6/9.
= 2/3.

Thanks.