a)
We are going to pick two cards at random from a deck of 52. Then, we have to multiply the number of choices for each card together.
for first card, there are 52 choices (all cards available), and we don't put the first card that we pick back into the deck before picking the second card, so we only have 52 - 1 = 51 choices for the second card.
n(S) = 52*51 = 2652
b)
n(A) = 20*19 =380
c) 20/52 * 19/51 = 0.14 = 14%