Math Reviews

http://www.quia.com/jg/66145.html.

http://www.geocities.com/multiplicationfacts/hardend.htmlhardend

http://quizhub.com/quiz/f-multiplication.cfm

www.aaamath.com/sub.html

http://arcytech.org/java/clock/clock.html

www.visualfractions.com

www.math.rice.edu/~lanius/fractions/frac.html