INTRODUCTION
have no divisor is 11. Such a number is, of course, called a prime
number.
The maxim that there is always a right way and a wrong way of
doing anything applies in a very marked degree to the solving of
puzzles. Here the wrong way consists in making aimless trials
without method, hoping to hit on the answer by accident, a process
that generally results in our getting hopelessly entangled in the trap
that has been artfully laid for us.
Occasionally, however, a problem is of such a character that,
though it may be solved immediately by trial, it is very difficult to
do by a process of pure reason. But in most cases the latter
method is the only one that gives any real pleasure.
When we sit down to solve a puzzle, the first thing to do is to
make sure, so far as we can, that we understand the conditions.
For if we do not understand what it is we have to do, we are not
very likely to succeed in doing it. We all know the story of the
man who was asked the question, "If a herring and a half cost
three-halfpence, how much will a dozen herrings cost ?" After
several unsuccessful attempts he gave it up, when the propounder
explained to him that a dozen herrings would cost a shilling.
" Herrings !" exclaimed the other apologetically, " I was working
it out in haddocks !"
It sometimes requires more care than the reader might suppose
so to word the conditions of a new puzzle that they are at once
clear and exact and not so prolix as to destroy all interest in the
thing. I remember once propounding a problem that required
something to be done in the " fewest possible straight lines," and a
person who was either very clever or very foolish (I have never
quite determined which) claimed to have solved it in only one
straight line, because, as she said, " I have taken care to make all
the others crooked ! " Who could have anticipated such a
quibble ?
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