A dealer shuffles a 52-card pack and turns up two cards at the same time. What is the probability that the pair matches in colour, that is, both red or both black?

Total = C(52,2) = 1326. Both red gives C(26,2) = 325 and both black another 325, so favourable = 650 and the probability is 650/1326 = 25/51. Trap 1/2 assumes the answer must be a half by symmetry, but removing the first card leaves 25 same-colour cards against 26 of the other colour, so a match is slightly LESS likely than a mismatch. Trap 25/102 counts only the red-red pairs. Trap 26/51 is the mismatch probability — note 25/51 + 26/51 = 1.