Kind Sir—

I teach 5th grade.

I see in my notes I once got some numbers related to the Impossible 15 Problem, but my notes do not show what this is.

Can you help?

Thanks!

Archie Lintz in Indiana

> I teach 5th grade.

It's a great responsibility, believe me.

> I see in my notes I once got some numbers related
> to the Impossible 15 Problem, but my notes do not
> show what this is.

Well, lift and swap any two counters to make the problem impossible. The game may be very entertaining and edifying if you succeed in presenting it right. Check the following URL's:

http://www.cut-the-knot.com/pythagoras/history15.html

http://www.cut-the-knot.com/Curriculum/Combinatorics/Fifteen.html

http://www.cut-the-knot.com/Curriculum/Combinatorics/MakeYourMove.html

Good luck,
Alexander Bogomolny