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In a small village, there are 87 families, of which 52 families have atmost 2 children. In a rural development programme 20 families are to be chosen for assistance, of which atleast 18 families must

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Question

In a small village, there are 87 families, of which 52 families have atmost 2 children. In a rural development programme 20 families are to be chosen for assistance, of which atleast 18 families must have at most 2 children. In how many ways can the choice be made?

Sum
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Solution

It is given that out of 87 families

52 families have at most 2 children

So other 35 families are of other type.

For rural development programme

20 families are to be chosen for assistance, of which at least 18 families must have atmost 2 children.

Thus, the following are the number of possible choices:

52C18 × 35C2 (18 families having atmost 2 children and 2 selected from other type of families)

52C19 × 35C2 (19 families having at most 2 children and 1 selected from other type of families)

52C20 (All selected 20 families having atmost 2 children)

Hence, the total number of possible choices is

52C18 × 35C2 + 52C19 × 35C2 + 35C1 + 52C20 

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Chapter 7: Permutations and Combinations - Solved Examples [Page 119]

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NCERT Exemplar Mathematics Exemplar [English] Class 11
Chapter 7 Permutations and Combinations
Solved Examples | Q 10 | Page 119

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