Students will learn how to find the number of combinations, with and without restrictions. Here's an example of finding the number of combinations without restrictions:

$$\displaystyle \binom{5}{3} = \mathop{?}$$

And here's an example problem having restrictions:

In how many ways can we fill four slots with the digits 1-8, such that two digits are odd and two digits are even?

After your students are proficient at finding combinations with and without restrictions, have them try this, then this, then this, then this, and finally, this.