We don't understand what you mean by "different marks". If you meant three cards like these, different ranks and different suits: J♥, 3♦♦, 8♣, then there are 13C3 ways to choose the 3 ranks, and for each of those ways, there are 4 suits to give the lowest-ranked card, and for each of those ways, there are 3 suits remaining to give the card with the middle-rank, and 2 suits remaining to give to the highest-ranked card. The numerator of the probability would be (13C3)(4)(3)(2) = 286*24 = 6864. The denominator would be the number of ways to select any 3 cards, or 52C3, or 22100. That would be a probability ofwhich reduces to , not . So we must be misinterpreting what you mean by "different marks". Sorry. Edwin