How To: Find the greatest common factor of two numbers

Looking for a guide on how to calculate the greatest common divisor for two numbers? 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). With this installment from Internet pedagogical superstar Salman Khan's series of free math tutorials, you'll learn how to calculate the greatest common factor (GCF or GCD) of two given integers in basic arithmetic.