Stage: 3 Challenge Level: 
Press the start button and see what happens:
This text is usually replaced by the Flash movie.
Now try again starting with a different number.
Try again.
Try starting with a fraction.. or decimal... or negative number...
Why is the answer ALWAYS the same?
Can you design instructions for similar machines of your own?
Using symbols. smartphone. Visualising. Linear equations. Generalising. Creating expressions/formulae. Mathematical reasoning & proof. Manipulating algebraic expressions/formulae. Introducing algebra. Area.
Published May 2004,October 2010.
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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