My question is: The library has 9,900 books. Over the summer, they sold some books. If only four sixths of the books are left, how many did they sell? Your thoughts:
A sixth of the books is 9900 / 6 = 1650 books. Only 4 * 1650 = 6600 books are left. The library sold 9900 - 6600 = 3300 books over the summer. The final answer: 3300.