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Counting Numbers
Natural Numbers are called counting numbers.Counting Principle of Multiplication
If a total event can be sub-divided into two or more independent sub-events, then the number of ways in which the total event can be accomplished is given by the product of the number of ways in which each sub-event can be accomplished.No. of ways in which the total event can be accomplished
= (No. of ways in which the 1st sub-event can be accomplished)
× (No. of ways in which the 2nd sub-event can be accomplished)
× (No. of ways in which the 3rd sub-event can be accomplished)
× ....
⇒ nE= nE1 × nE2 × nE3 × ....
| Eg: | 1. |
Consider the journey from "New Delhi" to "New York" via "London". There are four routes from "New Delhi" to "London" and five routes from "London" to "New York"
To find the number of ways in which a person can travel from New Delhi to New York, we can divide the total event of travelling from "New Delhi" to "New York" into two independent parts.
[The events are independent because, the route taken in one part journey is not dependent on the route taken on the other i.e. what route is taken is not influenced by what route has been taken in the other part journey]
There are four routes from "New Delhi" to "London" and five routes from "London" to "New York" ⇒ The number of ways in which the journey
Therefore,
= (No. of ways in which the journey from "New Delhi" to "Lodon" (1st sub-event) can be accomplished) × (No. of ways in which the journey from "London" to "New York" (2nd sub-event) can be accomplished)
ReasoningLet "A", "B", "C" and "D" represent the four routes from "New Delhi" to "London".Let "1", "2", "3", "4" and "5" be the numbers representing the routes from "London" to "New York". The possibilities can be summarised as
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| 2. |
Drawing 3 blue, 2 red and 4 white balls from a bag containing 6 blue, 4 red and 7 white balls.
Total number of balls = 17 [6 blue + 4 red + 7 white] Number of balls drawn = 9 [3 blue + 2 red + 4 white] To find the number of ways in which the 3 blue, 2 red and 4 white balls are drawn, we can divide the total event of drawing 9 balls into three sub-events
Therefore, The number of ways in which the 9 balls can be drawn such that 3 blue, 2 red and 4 white balls are drawn = (No. of ways in which the 3 blue balls (1st sub-event) can be drawn from the total 6) × (No. of ways in which the 2 red balls (2nd sub-event) can be drawn from the total 4) × (No. of ways in which the 4 white balls (3rd sub-event) can be drawn from the total 7)
This can be represented as
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| Author Credit : The Edifier | ... Continued Page :: 5 |
