Five cards are dealt at random and without replacement from a standard deck of 52 cards. What is the probability that the hand contains all 4 aces if it is known that it contains at least 3 aces?

i know the denominator includes the number of hands that contain 4 aces, (4 nCr 4)x(48 nCr 1) It also includes the number of hands that contain 3 aces and two other cards (4 nCr 3)x(48 nCr 2). But I am confused about numerator. I believe it is a question of conditional probability. Pls help.