Stage: 1 Challenge Level: 
A hundred square has been printed on both sides of a piece of paper. One square is directly behind the other.
What is on the back of $100$? $58$? $23$? $19$?
Can you see a pattern?
A poster of this problem is available here.
This problem is also available in French: Grille de 100Compound transformations. Tangram. Visualising. Interactivities. Working systematically. Patterned numbers. 100 square. Cubes. Games. Practical Activity.
Published September 2004,October 2009.
Copyright © 2007. University of Cambridge. All rights reserved.
NRICH is part of the family of activities in the Millennium Mathematics Project, which also includes the Plus and Motivate sites.
email: nrich@damtp.cam.ac.uk