Mind you, who else can. In everyday life, we rely on calculators and cash registers. but being able to do a little mental arithmetic is still useful. Especially with many Blackjack, Poker and many other strategy and games of chance. In roulette, it is hardly necessary for the game. You put your chips in and wait to see where the ball stays. But with a roulette strategy, mental arithmetic is useful. With the Labouchere system, you can write on a piece of paper...