Question

A person has $12$ friends and he wants to invite $8$ of them to a birthday party. Find how many times $3$ particular friends will always attend the parties.

Answer 1

Total $12$ friends are there

and $8$ has to be invited

$3$ particular has to be invited every time

So he has to choose to remain $5$ in remaining $9$ friends and that is possible in ${9_C}_5$ $=126$