# Sum of Probabilities

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The sumof the probabilities of all the elementary events of an experiment is one.

Example: take the coin-tossing experiment. P(Heads) + P(Tails )

Impossible Events

If there is no possibility of an event to occur then its probability is zero. This is known as an impossible event.

Example

It is not possible to draw a black ball from a group of red balls.

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