Question

In how many ways can a boy invite his 5 friends to a party so that at least three join the party?

Answer 1

The number of ways of inviting at least three friends from 5 friends

= `""^5"C"_3 + ""^5"C"_4 + ""^5"C"_5`

= `(5!)/((5 - 3)!3!) + (5!)/((5 - 4)!4!) + 1`

= `(5 xx 4)/(2xx 1) + 5  + 1`

= 10 + 5 + 1
= 16