[Talking_Mouse]

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[georgiadevildog]

From one math nerd to another: thanks! My mother the math teacher will surely love this one. Incidentally, ever use the "bridge" method to do the 11-19 times tables?

[Eepsy]

I think they must mean any two digit number /ending/ in five, not divisible. To find the square of any two digit number ending in zero, you simply square the first digit and add two zeros.

[Nick Danger]

Looks like a re-hash of Tractenberg.

[beef]

ping

[megatherium]

The Indians do have much to be proud of in terms of mathematics: they originated our base 10 number system (which we call Arabic, but the Arabs got it from India). They were very good at number theory and geometry. Forgive the following technical detail, but Indian mathematicians discovered power series for trigonometric functions before Western mathematicians. And many people are familiar with the amazing story of the early 20th century mathematician Ramanujan.

But allow me to say that this "Vedic mathematics" looks like a bunch of mystic mumbo-jumbo wrapped up in a collection of clever number tricks. I don't doubt the tricks work, and it might be fun to learn them, but someone with a serious interest in math would be much better off learning "western mathematics" (that actually the whole world now holds in common, from east Asia to the USA). If you've had university math through calculus, try to find a good intro number theory text. Many lovely theorems about numbers to amaze you. (If you haven't had calculus, but are very good at algebra, you might find an elementary number theory text that's accessible to you.)

[Calusa]

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[wideminded]

The book Dead Reckoning, Calculating Without Instruments by Ronald W. Doerfler is packed with calculation tricks like this one and many more sophisticated ones.