Bookworm  logic puzzle
A bookworm eats a straight way through a encyclopedia consisting of ten parts. Each part has 1000 pages. The bookworm starts on the front cover of the first part and ends on the back cover of the last part. From how many pages did the bookworm eat? 
Explanation
Assuming that the encyclopedia is ordered in the usual way, the row of books starts with the back side of part one and ends at the front side of part ten. If the bookworm starts at the front cover of part one it does not has to go through part one anymore, but starts immediately in part two. The worm follows the red way until part nine. Then the worm is on the back side of part ten. So the the bookworm eated from 8000 pages. 
