Stage: 2 Challenge Level: 
This one is a bit more of a puzzle.
Can you work out what happens in the three circles?
Factors and multiples. Trial and improvement. Investigations. Generalising. Interactivities. Combinations. Sequences. Multiplication & division. Addition & subtraction. Working systematically.
Published May 2005.
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