Exercise 1.

You have 9 presents to give to your 4 kids. How many ways can this be done if:

  1. The presents are identical, and each kid gets at least one present?

  2. The presents are identical, and some kids might get no presents?

  3. The presents are unique, and some kids might get no presents?

  4. The presents are unique and each kid gets at least one present?

in-context