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The law of large numbers says that the proportion of red should be close to the theoretical probability, which
is 47.37%. So we wouldn’t be surprised by 47 or 48 wins.
Another way to bet on a group of numbers is to place a square bet. By placing your chip on
the square formed by four numbers, you bet on all four of them.
In the following example, we will be betting on the square bet that contains the numbers
2,3,5, and 6. Here, you are betting on four numbers at once, so the probability of
winning is 4 out of 38.
Suppose you bet on both the square bet and on the red numbers, what is the
probability that you win at least one of your bets? That is, what is the probability
that the number that comes up is either red, or in this square, or both?
It seems reasonable to decide that the probability of winning at least one of your bets
should be the sum of the probabilities of each bet. Is this right? No.