A man has 9 friends, 4 boys and 5 girls. In how many ways can he invite them, if there have to be exactly 3 girls in the invitees?

3 girls can be be selected out of 5 girls in ⁵C₃ ways. Since, number of boys to be invited is not given, hence out of 4 boys, he can invite them in (2)⁴ ways.
∴ Required number of ways ⁵C₃ x (2)⁴ = 10 x 16 = 160