Combinations
Combination
Each of the groups or selections that can be made by taking some or all of a number of things without considering the arrangement or order is called a combination.
Thus, the selections that can be made by taking the letters a, b and c two at a time are three. i.e., ab, bc and ac. These three groups or selections are called the combination of three things taken two at a time.
The number of combinations of n dissimilar things taken r at a time is calculated using the expression
For Example: The number of selection of 6 dissimilar things taken 4 at a time is
The number of combinations of n dissimilar things taken all at a time is
Also,
For Example: The number of selection of 3 dissimilar things taken all at is a time
Illustration: Each person's performance compared with all other persons is to be done to rank them subjectively. How many comparisons are needed in total, if there are 11 persons ?
(a) 66 (b) 55 (c) 54 (d) 45
Answer : b
Solution Comparison is always done between two peoples, we have to select 2 persons among the 11 persons for a comparison. Hence
How many committee of five persons with a chairperson can be selected form 12 persons? | |||
| Right Option : B | |||
| View Explanation | |||
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