You have just
bought twelve postage stamps, in
this form : three by four.
A friend asks you to oblige him with four stamps, all joined together,
no stamp hanging on by a mere corner.
In how many
different ways is it possible for you
to tear off those four stamps?
You see, you can give him 1, 2, 3, 4, or 2, 3, 6, 7, or 1, 2, 3, 6, or
1, 2, 3, 7, or 2, 3, 4, 8, and so on.
Can you count the number of different ways in which those four stamps
might be delivered?
There are not many more than fifty ways.
Can you get the exact number?