The application of this rule is so easy that
it is needless to illustrate it by an example.
A THIRD WAY
Ask the person to add 1 to the triple of the number thought of, and
to multiply the sum by three; then bid him add to this product the
number thought of, and the result will be a sum from which if 3 be
subtracted, the remainder will be ten times the number required; and
if the cipher on the right be cut off from the remainder, the other
figure will indicate the number sought.
Example--Let the number thought of be 6, the triple of which is 18;
and if 1 be added, it makes 19; the triple of this last number is 57,
and if 6 be added it makes 63, from which if 3 be subtracted, the
remainder will be 60; now, if the cipher on the right be cut off, the
remaining figure, 6, will be the number required.
A FOURTH WAY
Tell the person to multiply the number thought of by itself; then
desire him to add 1 to the number thought of, and to multiply it also
by itself; in the last place, ask him to tell the difference of these
two products, which will certainly be an odd number, and the least
half of it will be the number required.
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