Source: http://www.arcademicskillbuilders.com/games/ratio-blaster/ratio-blaster.html
A couple of fun interactive websites (including the alien game)
http://www.arcademicskillbuilders.com/games/ratio-blaster/ratio-blaster.html
http://www.learnalberta.ca/content/mec/flash/index.html?url=Data/4/B/A4B2.swf