I've been reading up vedic maths the last few weeks and its an absolutely fascinating topic. It basically consists of 16 formulae as written down in age-old sutra's of India and allows for very easy mental calculation of complex division, multiplication, square roots etc.
Just a few basic examples to whet your appetite:
Multiply a two-figure number by 11 This couldn't be easier -- you simply put the sum of the first and last figure inbetween.
72 x 11 = 7 (7+2) 2 = 792
If the sum of the two figures is greater than 9 you simply carry the first figure of the sum and add it to to first figure of your number.
79 x 11 = 7 (7+9) 9 = 7 (16) 9 = 869
Dividing by 9 Here the answer for a two-figure number is the first figure as the result and the sum of the two figures the remainder.
23 / 9 result 2 remainder 2+3 = 5
For dividing three-figure numbers you need to add the sum of the first two numbers to the first figure and the total sum of the three numbers is your remainder.
134 / 9 result 1 (1+3) = 14 remainder (1+3+4) = 8
It is amazing to how these simple rules work and have noticed myself using some of them for quick multiplication etc. The only problem I often have is remembering what exact rule to use in what situation ;)
If I'd been taught basic maths using these techniques I definitely would've found it a lot more interesting -- just rediscovered the hidden beauty in numbers.
If you want to read up on it some more and take some interactive tutorials vedicmaths.org is a good place to start.