How many ways 12 books can be arranged 3 at a time?

Well, honey, if you want to arrange 12 books 3 at a time, that's just a fancy way of asking for a permutation. So, you've got 12 choices for the first book, 11 choices for the second book, and 10 choices for the third book. Multiply those together and you get 1,320 ways to arrange those books. Easy peasy lemon squeezy!