### 11 Answers

- JOHNLv 78 months ago
EDIT: For the benefit of the unenlightened one who saw fit to give this answer a TD.

The identity (10p + q)(10r + s) = 100pr + 10(ps + qr) + qs (0 ≤ p, q, r, s ≤ 9) is the basis of the scribblings below. The way the method works in practice is as follows. Take 89 x 67. Multiply last two digits; you get a 3 for the last digit of the answer with a 6 to be carried forward to the tens; take the cross products and add; you get 8 x 7 + 9 x 6 = 110; taking into account the c/f 6, we get 6 in the tens space with an 11 c/f; finally multiply the two 1st digits; with the 11 c/f we get 59 (8 x 6 + 11). Answer 5963. The method works for any 2-digit numbers. You don't have to know the rationale for the method to apply it - you can do so by rote. I had assumed that the people on this forum are sophisticated enough to work out for themselves the mathematical basis of what I did. I reckon you can train a chimpanzee to so sums of this sort, since one doesn't really need to go into the justification.

3 x 3 = 9 units

3 x 7 + 8 x 3 = 45 = 5 tens and 4 hundreds

8 x 7 = 56 hundreds

Add the 4 hundreds = 60 hundreds

Answer = 6059

(All of you should be able to do the first four steps in your heads and write the answer down in one go; my 3-year old granddaughter can do it).

lol

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- SumDudeLv 78 months ago
grab a clean piece of paper and a sharp pencil and do what you learned in 4th grad.

Source(s): No math skills means no high paying job.pencils are a thing of the past

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- PuzzlingLv 78 months ago
83 * 73

= (80 + 3)(70 + 3)

= (80*70) + (80*3) + (70*3) + (3*3)

= 5600 + 240 + 210 + 9

= 5600 + 459

= 6059

Source(s): https://youtu.be/UgrD0yfYPCo- ...Show all comments
Exactly!

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- PhilipLv 68 months ago
83*73 = 83(83-10) = (80+3)^2 -830 = 6409+480-830 = 6889 -830 = 6059.

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- Anonymous8 months ago
Skippy's calculator broken?

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- Anonymous8 months ago
Something that can be very easily figured out by using a calculator

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if this user has to ask on here without even thinking to use a calculator, they definitely lack the brain power to do that.

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use your brain. No batteries needed.