In a bookshelf, four volumes of Astrid Lindgren's collected works stand in order, with 200 pages in each volume. A worm living in this collection gnawed its way from the first page of the first volume to the last page of the fourth volume. How many pages did the worm gnaw through?

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Try to recall how volumes from a collected works set stand on a bookshelf.

## Solution

Note that when the volumes are placed in order on the shelf, the first page of the 1st volume touches the last page of the 2nd volume, and the last page of the 4th volume touches the first page of the 3rd volume. Thus, the worm only chewed through the 2nd and 3rd volumes, i.e., 400 pages.

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