10. A bookshelf with 3 shelves has 17 books on the top shelf, 15 books on the middle shelf, and 7 books on the bottom shelf. Monica wants each shelf to have the same number of books. She also wants to move as few books as possible. How many books should she move from the middle shelf to the bottom shelf? Pause if you want to try and solve it. Okay, so first things first, let's try to figure out how many books she wants to have on each shelf. So 17 plus 15 plus 7. 17 plus 15 is 32, and 32 plus 7 is 39. And if we divide that by 3, if we, excuse me, if we take 39 and divide that by 3, then that is going to be equal to 13. So there's going to be 13 books on each shelf. And so since there's more than 13 books on the middle shelf, we're just going to move books from the middle shelf to the bottom shelf, which is the one that has less than 13 books. So we can actually just see that since there's 15 books on the middle shelf and we want to have 13, we're going to move 2 of these to the bottom shelf, right? That'll leave 13 books on the middle shelf, and that'll be now 9 books on the bottom shelf. And then also if we move 17 minus 13 is 4. So if we take 4 of these books on the top shelf and move them to the bottom shelf, it's another 4. Well, 4 plus 9 is 13, which leaves us with, if I draw in a couple more books here, now we have 13 books on the bottom shelf, we have 13 books on the top shelf, and we have 13 books on the middle shelf. So the number of books that we moved from the middle shelf to the bottom shelf was 2. So the answer is option B, which is 2.

book distribution

shelf balancing

minimal moves

even distribution

shelf organization