In Blackjack, math is used to calculate the probability of outcomes by analyzing the composition of the deck and the likelihood of drawing specific cards. Players consider the number of high and low cards left, which helps them assess their chances of winning, losing, or getting a blackjack. These probabilities vary based on factors like the number of decks in use and actions taken during the game. By applying statistical calculations, players can make informed decisions about when to hit, stand, double down, or split, ultimately improving their chances of winning while managing risk more effectively.