Basic rules of probability The was an error performing the Search. Please try again later.
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These are some basic rules of probability that can be applied to a game of poker:

1. The probability of an event occurring plus the probability of the event not occurring equals 1.

If, for example, the chance of getting a heart on the next card is 1 in 5 (20%), then the chance of not getting a heart is 4 in 5 (80%). Understanding and remembering this rule allows a player to calculate the probability of an event by calculating its opposite (sometimes one way is easier than the other).

2. The probability of two events both occurring is the probability of the first occurring multiplied by the probability of the second occurring, given that the first has already occurred.

Put simply, the chances if flipping a coin and it landing heads up is 1 in 2 (50%). The chances of it happening a second time straight is 1 in 4, therefore 1 / 2 x 1 / 2 = 1 / 4.

The practical importance of this is that since probabilities are all less than one, the probability of a sequence of events all happening is smaller than the probability of any single one of them.

3. The probability of either of two events occurring is the probability of the first occurring plus the probability of the second occurring minus the probability of both occurring.

For example, if you asking about the probability of either a straight or a flush in five cards, you must recognise that some hands (namely straight flushes) are both and thus would be counted twice.