Question 381230
We're given that event A has occurred, which means that we know that a queen has been selected. There are 4 queens (one of each suit) and only one queen of diamonds. So P(B | A) = {{{1/4}}}



Formally, P(B | A) = P(A intersect B)/P(A), so this means that P(B | A) = P(Queen and diamond)/P(Queen) = (1/52)/(4/52) = 1/4