hi,

there are some assumptions behind your formula, that might be right or wrong. It seems like you have 22 trials and at the end of each trial the winner leaves the game, everybody else stays. Then the probability that the first game will be won by a black shirt would be 70/88 (not 66/88 BTW). The next trial will be run with 87 participants from which there are 18 red shirtd so the probability that a black shirt wins will be 69/87, for the third game it will be 68/86 and so on. The probability of all of this happening will be the product of the individual probabilities 70/88*69/87*...*(70-21)/(88-21)

regards