Suppose that you have 4 green cards and 5 yellow cards. The cards are well shuffled. You randomly draw two cards without replacement.

Question

P(At least 1 green) =

Answer 1

P(at least 1 green) = 1 - P(no green)

P(no green) = draw yellow on both draws = P(draw yellow on 1st draw) * P( draw yellow on 2nd draw, given draw yellow on 1st draw) = 5/9 * 4/8 = 20/72 = 5/18

P(at least 1 green) = 1 - 5/18 = 13/18