B

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If a coin is tossed in the air. It is not certain that an head will appear. However, suppose we repeat this experiment, let S be the number of incoming head and let N be the number of tosses, then the ratio S/N becomes stable after long run.

The probability P of a an event A is defined as follows: if A can occur in S ways out of a total N equally likely ways, then

P = S / N