In the illustration Professor Rackbrane is seen demonstrating
one of the little posers with which he is accustomed to
entertain his class. He believes that by taking his pupils off
the beaten tracks he is the better able to secure their
attention, and to induce original and ingenious methods of
thought. He has, it will be seen, just shown how four 5's may be
written with simple arithmetical signs so as to represent 100.
Every juvenile reader will see at a glance that his example is
quite correct. Now, what he wants you to do is this: Arrange
four 7's (neither more nor less) with arithmetical signs so that
they shall represent 100. If he had said we were to use four 9's
we might at once have written 999/9, but the four 7's call for
rather more ingenuity. Can you discover the