Introduction Of Combinations MCQ - Practice Questions & Answers

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INTRODUCTION OF COMBINATIONS is considered one the most difficult concept.
179 Questions around this concept.

Concepts Covered - 1

INTRODUCTION OF COMBINATIONS

So far our task was always to “arrange” objects i.e. to place them in a specific order among themselves.

Sometimes we would be interested in only “selecting” a few objects out of the given objects. In this case, we just need to “select” and we do not need to “arrange” them in an order.

The notation of selecting r objects from n given object is ${ }^{\mathrm{n}} \mathrm{C}_{\mathrm{r}}$.

${ }^{\mathrm{n}} \mathrm{C}_{\mathrm{r}} = \frac{n!}{(n-r)!\cdot r!}$

Multiplication Rule

If a certain work W can be completed by doing 2 tasks, first doing task A AND then doing task B. A can be done in m ways and following that B can be done in n ways, then the number of ways of doing the work W is (m x n) ways.

Addition Rule

If work W can be completed by doing task A OR task B, and A can be done in m ways and B can be done in n ways (and both cannot occur simultaneously: in this case we call tasks A and B as mutually exclusive), then work W can be done in (m + n) ways.