>>13056065Yes, but you assumed that A is heads, wich isn't neccesarily the case, what you actually have is that you know that atleast one coin is heads:
>Atleast one coin is headsP(A)=3/4
>Both coins are headsP(B)=1/4
P(B|A) = P(B&A)/P(A)
But since P(B&A) = P(B) we get
P(B|A) = P(B)/P(A) = (1/4)/(3/4) = 1/3.
Think about it this way. Your friend flips two coins and tells you that atleast one is a heads, you hence know that there are 3 possibilities, all equally likely, only one gives the desired result. So then you know that the probability is 1/3.
What your calculations shoq is that your friend flipped one of the two coins and got heads, then told you he got heads, then flipped the other coin, or equivilently, flippwd the first coin, got heads, then flipped the 2nd and told you thw first was heads.
