<p>Here’s a problem to get you started? How many ways can you arrange the word “PEN”?</p>
<p>The answer is 6, because there are 3 possibilities for the first letter, 2 for the 2nd, and 1 for the third. And of course, you’d multiply, because for each first letter, there are 2 possible 2nds and 1 third. Also, tree diagrams can really, really help!</p>