In a village, there are 87 families of which 52 families have at most 2 children. In a rural development programme, 20 families are to be helped chosen for assistance, of which at least 18 families must have at most 2 children. In how many ways can the choice be made?
Given that 52 families out of 82 families have at most 2 children.
It is told that 20 families need to be selected with at least 18 families having utmost 2 children.
The following are the cases:
i. 18 families having at most 2 children and 2 from other families
ii. 19 families are having at most 2 children and 1 from other families
iii. 20 families having at most 2 children
Let us assume that the no. of ways choosing to be N.
⇒ N = (Selecting 18 families having at most 2 children and 2 from other families) + (Selecting 19 families having at most 2 children and 1 from other families) + (Selecting 20 families having at most 2 children)
⇒ N = (52C18 × 35C2) + (52C19 × 35C1) + (52C20)
We know that ,
And also n! = (n)(n – 1)......2.1
⇒
⇒
⇒
⇒
⇒
∴ The no. of ways of choosing 18 families are .