Chanced upon this YouTube video on an interesting way of solving multiplication problems.

Admittedly, this is the first time Miss Loi is seeing this and she thought this might be useful for your anti-careless-mistake-checking procedure in E-Maths Paper 1 (where calculators are taboo).

But then again it’s now well past midnight and Miss Loi is too exhausted after a day of tuition to try this herself. As such she needs a volunteer immediately to try out 1298475326589 X 3055978070712 *types with eyes closed* and see if it works. First one to inform Miss Loi will stand to win a ~~romantic dinner~~ ~~pair of movie tickets~~ … errr … a big and much sought-after and emotional “Well Done & Keep It Up!” message from her.

Hmmm … wonder if they have something similar for division?

Thanks to this blog for the heads up!

## 14 Comments

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Wow, thats a really cool method Ms Loi, I enjoyed watching this 🙂

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Good morning marina!

So you managed to see if this works for 1298475326589 * 3055978070712 already? 🙂

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An amazing graphical interpretation of multiplication by breaking the digits up. Once you know why this works, it can be used for polynomial multiplication too!

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So that's mathematicians do, eh? That's pretty amazing, really.. Thanks for the video.

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yk, are you a maths major?

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love it.. love it.. love it..

but mr loi, isn't it a little bit cruel to ask whether it works for 1298475326589 x 3055978070712?

can imagine counting over 3.968 septillion dots (or 3,968,112,123,416 trillion dots)?? makes me wonder if u regularly torture ur students this way.. haha..

haha.. anyway, love the video..

=)

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oops, should be *Ms.. haha.. my mistake.. sorry..

=)

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haha actually no. My major's in Computer Science, so the maths I deal with is usually discrete.

On my comment, it could be a quick way to check your polynomial "factorisation" too.

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ok wait on second thoughts, it might be harder to deal with negative coefficients. :S

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nay min thu:

Yes Mr Loi is a sadistic twisted evil tutor who takes particular glee in traumatizing his students with maths problems such as 1298475326589 x 3055978070712 (without the use of a calculator).

Miss Loi, on the other hand, is a sweet, gentle and caring tutor who provides Mr Loi with such maths problems 🙂

Oh well she's babbling nonsense again ...

Thanks for dropping by!

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I also learned a special one during my childhood.

It can be apply to any 25X25, 35X35 etc. Just add one to the first digit. the final 2 digit is 25.

E.g. 75X75 is 8X7=56. The answer is 5625. Cheers!

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lostin,

How come Miss Loi never learn this in her childhood??? Do you have any more of such tricks up your sleeve?

Maybe we should consolidate all of our special quirky mathematical tricks in one place and let the students pick the most suitable one depending on the scenario.

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Nice trick! I have one for 11 multiplication also.

Say we want to multiply the number abcd (NOT a*b*c*d) by 11.

Ones place: d

Tens place: c+d (if >10, keep the ones place and carry 1)

Hundreds place: b+c (+1, if the tens place got carry one, and again if total >10, keep the ones and carry 1)

Thousands place: a+b (+1, if the hundreds place got carry one, and again if total >10, keep the ones and carry 1)

Ten-thousands place: a (+1, if the thousands place got carry one)

Example: 2392 x 11

Ones place: 2

Tens place: 9+1=11, so tens place is [1] and carry 1

Hundreds place: 3+9+1 (cos just now carry 1) =13, so hundreds place is [3] and carry 1.

Thousands place: 2+3+1 (cos just now carry 1) =6

Ten thousands place: 2

Answer: 26312

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hey it was really nice trick ms. loi

but, how can i solve e.g 69*89?