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# Math training - how do you do it?

mental math
Recent activity on Jan 31, 2017
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Hi guys,

I have been using the Math Tool for a while now (easy/medium-random level) and I am really improving! Everything on the easy level is fine (matter of training) but I am looking for some math tricks on the medium-level questions.

So things to solve 1243/17=? or 1334*21, etc.

I struggle with the approach for these multiplications, and am aware there is some tricks for this. Any good websites you guys know of with tricks (metal math) to solve these questions?

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Thanks for the replies guys!

I know (and use) caseinterviewmath.com as well. A good website indeed, but only for practicing. They don't provide "tips and tricks" on how to solve sums like the aforementioned. Of course, one way is to use paper, and this might indeed be enough for cases. But if someone does know some "tips and tricks" I would love to hear of them (also, some of these tricks might have to be performed on paper as well).

An example of the tricks I am referring to:

- 227 : 5 = ? Instead of computing it the long way (7*5+20*5+200*5) you can multiple the first number by 10 (to make 2270) and than take half of it (1135, which is the answer). Goes for any division by 5 obviously.

- 19*18 = ? Although this one is easy to do the conventional way, an alternative is the trick of (1) adding the first digit of the lowest number to the highest number (= 8 +19 = 27), then (2) multiply this by 10 (= 27 * 10 = 270) and then (3) adding the product of the first two digits of both numbers (= 9 * 8 = 72), resulting in 270 + 72 = 342. This only works up to a multiplication of the numbers UNDER 20.

I would do this in another way: First calculate 18*20= 360 which is easy, and then subtract 18 from it 360-18 = 342

There are books that teach those kinds of tricks. It's been a while since I've read one, but Rapid Math Tricks is an example book. You might find it at a library.