Vedic Math
Rajesh Amin was the first to tell me about these amazing mathematical feats of the Vedic period in India, in which he contended differential calculus had a distant cousin. He said that in complete seriousness, as we strolled through the display of the British Museum, wondering about lost knowledge and wars. And now, it seems that part of this knowledge is surfacing out as tricks for the harried Indian students that want to get into universities, striving to gain any advantage:
"Obviously Vedic math cannot teach you how to solve a problem. But it greatly reduces the computing time. I can vouch for the fact that in a two-hour exam, I can save about 10 minutes using Vedic math."
via Mark Tosczak
UPDATE: Since Mark wants to study these online, probably an excursion to this site is in order.
Regrettably, the books are all gone. As happens to all nice books.