Our friend in the illustration has a large sheet
of zinc, measuring (before cutting) eight feet by three feet, and he
has cut out square pieces (all of the same size) from the four corners
and now proposes to fold up the sides, solder the edges, and make a
But the point that puzzles him is this: Has he cut out those square
pieces of the correct size in order that the cistern may hold the
greatest possible quantity of water?
You see, if you cut them very small you get a very
shallow cistern; if you
cut them large you get a tall and slender one.
It is all a question of finding a way of cutting put these four square
pieces exactly the right size.
How do you avoid making them too small or too