Where can I find sites that teach you how to calculate more complex numbers in your head?

Question

I'm looking for sites that teach you some math tricks and shortcuts that allow you to do more complex calculations in your head without the need of a computer or calculator. For instance, one trick I know is multiplying any two-digit number by 11. To do that: take the two numbers and add them up, then put the result in the middle. Example: 11 * 62 means that you should add up 6 and 2 then put the result between them, which would make it 682. If they add up to more than 9, put the right digit in the middle and add the left digit (of the result) to the left digit of the number you're multiplying by 11. Example: 11 * 69 means adding 6 and 9 (resulting in 15). Now put the 9 at the right where it is, then put the 5 in the middle and add the 1 to the 6 = 759. (Try it on the calculator.)

That's what I'm talking about. I'm looking for a site(s) that teaches you things like that. Anyone know anything like that?

Answer 1

http://www.hinduism.co.za/vedic.htm#What%20is%20Vedic%20Mathematics?

Answer 2

Try mathworld.

Answer 3

try wikipedia or wikihow