(related to Problem: The Industrious Bookworm)
The hasty reader will assume that the bookworm, in boring from the first to the last page of a book in three volumes, standing in their proper order on the shelves, has to go through all three volumes and four covers. This, in our case, would mean a distance of $9\frac 12$ in., which is a long way from the correct answer. You will find, on examining any three consecutive volumes on your shelves, that the first page of Vol. I. and the last page of Vol. III. are actually the pages that are nearest to Vol. II., so that the worm would only have to penetrate four covers (together, $\frac 12$ in.) and the leaves in the second volume ($3$ in.), or a distance of $3\frac 12$ inches, in order to tunnel from the first page to the last.
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