<p>^because it asked for COMBINATIONS, not ARRANGEMENTS. “Permutation” is a synonym for “arrangement”.</p>
<p>There are 6 permutations but they can be written in pairs: 12, 21 and 13,31 and 23,32. So there are 6 permutations but only 3 combinations.</p>
<p>Also, this is one of those cases where it helps to realize that selecting combinations of two items from a list of 3 is the same as selecting the ONE item that you leave out. And there are clearly 3 ways to do that…</p>