MISCELLANEOUS PUZZLES
91.—
The Five Tea-Tins.
Sometimes people will speak of mere counting as one of the
simplest operations in the world ; but on occasions, as I shall show,
it is far from easy. Sometimes the labour can be diminished by the
use of little artifices ; sometimes it is practically impossible to make
the required enumeration without having a very clear head indeed.
An ordinary child, buying twelve postage-stamps, will almost in-
stinctively say, when he sees there are four along one side and three
along the other, " Four times three are twelve," while his tiny
brother will count them all in rows, "1,2, 3, 4," &c. If the child's
mother has occasion to add up the numbers 1, 2, 3, up to 50, she
will most probably make a long addition sum of the fifty numbers,
while her husband (more used to arithmetical operations) will see at
a glance that by joining the numbers at the extremes there are
25 pairs of 51 ; therefore, 25 x 51 = 1,275. But his smart son of
twenty may go one better and say, "Why multiply by 25 ? Just
add two 0's to the
51 and divide by 4,
and there you
are !"
A tea merchant
has five tin tea-
boxes of cubical
shape, which he
keeps on his counter
in a row, as shown
in our illustration.
Every box has a
picture on each of
its six sides, so
there are thirty pic-
tures
m all; but
one picture on
No. 1 is repeated on No. 4, and two other pictures on No. 4 are
repeated on No. 3. There are, therefore, only twenty-seven differ-
107
