Most people can't do mental arithmetic any more. What a pity indeed :-(
Almost everyone relies on calculators these days. So today I'm going to tell you how to do an apparently difficult feat of mental arithmetic. Today you will learn how to take integer Cube Roots in your head! It's really dead easy, believe me!
Go to this blog post for the technique
Coincidentally, I was just reading a page on Vedic math techniques today. I have many Indian coworkers, and one of them is a woman who is as interested in math puzzles as I am. She is a whiz at mental calculations.
ReplyDeleteMy coworker and I have been discussing the differences between US and Indian math instruction. She has an 11-year-old daughter who is also a math brain, so she is especially interested in comparing and contrasting.
For example: Indian children learn to square numbers ending in 5 in their heads, using the fact that x^2 = (x-5)(x+5) + 25. For example, 25^2 = 20(30)+25, or 625. She demonstrated by squaring 145. She worked it out loud as follows: 14 squared is 196, plus 14 is 210, so 21025 is the answer.
I told her that here they only teach the algorithmic methods of multiplication, and in fact they barely teach those anymore, as many students require a calculator to multiple single-digit numbers. She indicated that in India they memorize the times tables up to 15 or 20. I told her that in my day we memorized MAYBE up to 12.
We have traded puzzle books for the weekend. I lent her a Dudeney, a Gardner, and an Emmet, and she's lent me one by Shakuntala Devi.
typo in 2nd-to-last para: multiple = multiply
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