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?
A sixth of the books is 9900/6 = <T>divide(9900, 6)=1650.0 books.
Only 4*1650 = <T>multiply(4, 1650)=6600 books are left.
The library sold 9900-6600= <T>subtract(9900, 6600)=3300 books over the summer.
