Everyone has an intuitive idea of what is meant by the words ‘Probable’ and ‘Probability’. The dictionary meaning of the word ‘Probability’ is ‘likely though not certain to occur’.

Have you ever noticed:-

• How many phone calls we attend in one day?

• How many times we visit the switchboard at our home?

• How many choices we made while choosing our dress for the day?

• How many times we go out for a dinner in a month?

• How many times we obtain head in five tosses of a coin?

• How many times we obtain the number 5 in six throws of an unbiased die?

So there is an element of unpredictability in many physical phenomena. Even under apparentely identical conditions, many observed quantities vary in an uncertain way. There are various situations in which a particular result or outcomes not certain, but it can be any one of the several possible outcomes.

Before giving final shape to the definition of probability lets consider the following simple experiments:-

Expt 1:- A coin is tossed and the result is noted.

Expt 2:- A card is drawn from a well shuffled pack of 52 playing cards and its colour is noted.

In either experiment , there is not single definite outcome. When a coin is tossed it may show head up or tail up. We cannot say beforehand whether it will show head up or tail up. That depends on ‘chance’.

Similarly , a card drawn from a well shuffled pack of 52 playing

cards may be red or black. That again depends on ‘chance’.

Such phenomena are called ‘Probabilistic’. “The Theory of Probability ”is concerned with this type of phenomena.

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