Look for an easy way to find the least (or lowest) common multiple for a set of numbers? Like to think in pictures? Try the upside-down birthday cake method! Learn how with this free video lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).