Key Points - Probability

- Probability: If there are n elementary events associated with a random experiment and m of them are favourable to an event A then the probability of happening of event A is defined as the ratio

-  m and is denoted by P(A). n

The Theoretical probability of an event E written as (E) is
P(E)= Number of outcomes favourable of E / Number of all possible outcomes of the exp eriment

- The sum of the probability of all the elementary events of an experiment is 1.

- The probability of a sure event is 1 and probability of an impossible event is 0.

- If E is an event, in general, it is true that (E) + P (E ) = 1.

- From the definition of the probability, the numerator is always less than or equal to the denominator therefore 0 ≤ P ( E ) ≤ 1 .

- Elementary Event: An outcome of a random experiment is called an elementary event.

- Compound Event: An event associated to a random experiment is a compound event, if it is obtained by combining two or more elementary events associated to the random experiment.

- Sure Event: Those events whose probability is one.

- Impossible Event: Those events whose probability is zero.

- Occurrence of an Event: An event A associated to a random experiment is said to occur, if any one of the elementary events associated to the event A is an outcome.