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The probability of an event occurring is a measurement of how likely the event is to occur. If two events A and B have equal probabilities, then we say that A and B are equally likely.

For example, in rolling a single die, the events "rolling a 4" and "rolling a 5" are equally likely. However, in drawing a single card from a standard deck of cards, drawing a Heart is more likely than drawing a King, since

P(Heart)=\frac{1}{4}   and   P(King)=\frac{1}{13}.