Counting Techniques for PreCalculus
Counting the number of ways to perform a task is fairly simple — until the number of choices gets too large. Here are three counting techniques used in precalculus:

Permutations: How many ways you can choose r things from a total of n things when the order of your choices matters

Combinations: How many ways you can choose r things from a total of n things when the order of your choices doesn’t matter

Multiplication principle: How many different possibilities exist if you choose 1 from a things, 1 from b things, 1 from c things, 1 from d things, and so on.
Use the following formulas for these counting techniques: