Clock arithmetic and modular arithmetic

http://www.shodor.org/interactivate/discussions/morerem.html

This site gives a nice introduction to modular arithmetic.

http://betterexplained.com/articles/fun-with-modular-arithmetic/

This site is a nice interactive site which deals with arithmetic (mod *m*). Do not be frightened by the notation, the arithmetic table at the bottom is interesting

http://www.cut-the-knot.com/blue/Modulo.shtml

Is there really such a thing as “infinity”?

http://www.math.toronto.edu/mathnet/plain/answers/infinity.html