Lifechangers: The Khan Academy, Changing the Face of Learning

"Extra" caught up with Bill Gates' favorite teacher Salman Khan, who created, a free tutorial website that's changing way we learn.

Khan, who graduated from MIT and boasts an MBA from Harvard, started the free virtual school for the world after turning down a million dollar job at a hedge fund. The popular learning site gets around 70 thousand hits a day and has received 18 million views since it launched four years ago.

"There's a ton of people watching it in India, South Korea, Italy, Scandinavia, New Zealand, I mean, all over. It's pretty much mind boggling," Salman explained.

The site, which was conceived from the closet of his Silicon Valley bedroom, features everything from organic chemistry to the Pythagorean theorem video and is part of the new digital age of teacher-student learning where a user can watch, practice, and learn almost anything, for free.

Khan goes on to say, "Everyone gets to watch exactly at their level, at their speed. If they're shaky on a subject they should have learned three years ago, they can watch a video on that. They don't have to feel embarrassed about that."

The site is so popular, billionaire Bill Gates praised it when we spoke to him at the Aspen Film Festival. "There's this website I've been using with my kids called ... just one guy doing some unbelievable 15-minute tutorials."