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 9½ 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, ½ in.) and the leaves in the second volume (3 in.),
or a distance of 3½ inches, in order to tunnel from the first page to
the last.