There are six books on a bookshelf, arranged in order from volume 1 to volume 6. Each of the books is 2.5" thick, including the covers, each of which are 0.25" thick. A bookworm eats through the books in a straight horizontal line beginning at the front cover of the first volume and ending at the back cover of the sixth volume. How many inches did the bookworm travel?
inches

The bookworm travels 10.5 inches. The path that the bookworm would have taken is to eat through the front cover of volume 1, through volumes 2, 3, 4, and 5 in their entirety, and the back cover of volume 6. So, the distance travelled would be 0.25 + 4 × 2.5 + 0.25 = 10.5 inches.

Source

This problem is based on one given in More Joy of Mathematics by Theoni Pappas, page 13.