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