If we were to write n factorial, let me see how we can write this. If we were to write n factorial, n factorial would be equal to n times n minus 1 times n minus 2, all the way down to 1. That's kind of what we want. We just want the first k terms of it. What if we divide this by n minus k factorial? Let's think about what that is going to do. If we have n minus k factorial, that is the same thing as n minus k times n minus k minus 1 times n minus k times n minus k minus 2, all the way down to 1.