- #1
semidevil
- 157
- 2
so P(A|B) = P(A intersect B)/ P(B).
so, P(A intersect B) is the same as P(A) * P(B) right? so doesn't the P(B) always cancel out, and the answer will always be P(A)? That doesn't makes sense at all...
for example: A family has 2 children, and all possibilites are equally possible.
boy boy, boy girl, girl girl, girl boy.
what is the probability of getting Both boys, given that at least one is a boy.
==========================================
ok, so since each is equally possible, then there is 1/4 chance for each outcome.
and to have at least one boy, there is 2 chances, out of the 4 chances, which makes that 1/2.
so plug in the formula, and I get the wrong answer...(1/4 * 1/2)/1/4...which is wrong...
the book says the answer is 1/3...
so how do they do that? I don't understand the formula.
so, P(A intersect B) is the same as P(A) * P(B) right? so doesn't the P(B) always cancel out, and the answer will always be P(A)? That doesn't makes sense at all...
for example: A family has 2 children, and all possibilites are equally possible.
boy boy, boy girl, girl girl, girl boy.
what is the probability of getting Both boys, given that at least one is a boy.
==========================================
ok, so since each is equally possible, then there is 1/4 chance for each outcome.
and to have at least one boy, there is 2 chances, out of the 4 chances, which makes that 1/2.
so plug in the formula, and I get the wrong answer...(1/4 * 1/2)/1/4...which is wrong...
the book says the answer is 1/3...
so how do they do that? I don't understand the formula.