Question : A hat contains a number of cards with 30% white on both sides, 50% black on one side and white on the other side, 20% black on both sides. The cards are mixed up, and a single card is drawn at random and placed on the table. Its upper side shows up black. The probability that its other side is also black is
(A) 2/9
(B) 4/9
(C) 2/3
(D) 2/7
Answer : option
Solution :
