Impress your friends with mental Math tricks

November 11th, 2007 | by Sol |

See Math tricks on video at the Wild About Math! mathcasts page.

_____________________

Being able to perform arithmetic quickly and mentally can greatly boost your self-esteem, especially if you don’t consider yourself to be very good at Math. And, getting comfortable with arithmetic might just motivate you to dive deeper into other things mathematical.

This article presents nine ideas that will hopefully get you to look at arithmetic as a game, one in which you can see patterns among numbers and pick then apply the right trick to quickly doing the calculation.

The tricks in this article all involve multiplication.

Don’t be discouraged if the tricks seem difficult at first. Learn one trick at a time. Read the description, explanation, and examples several times for each technique you’re learning. Then make up some of your own examples and practice the technique.

As you learn and practice the tricks make sure you check your results by doing multiplication the way you’re used to, until the tricks start to become second nature. Checking your results is critically important: the last thing you want to do is learn the tricks incorrectly.

1. Multiplying by 9, or 99, or 999

Multiplying by 9 is really multiplying by 10-1.

So, 9×9 is just 9x(10-1) which is 9×10-9 which is 90-9 or 81.

Let’s try a harder example: 46×9 = 46×10-46 = 460-46 = 414.

One more example: 68×9 = 680-68 = 612.

To multiply by 99, you multiply by 100-1.

So, 46×99 = 46x(100-1) = 4600-46 = 4554.

Multiplying by 999 is similar to multiplying by 9 and by 99.

38×999 = 38x(1000-1) = 38000-38 = 37962.

2. Multiplying by 11

To multiply a number by 11 you add pairs of numbers next to each other, except for the numbers on the edges.

Let me illustrate:

To multiply 436 by 11 go from right to left.

First write down the 6 then add 6 to its neighbor on the left, 3, to get 9.

Write down 9 to the left of 6.

Then add 4 to 3 to get 7. Write down 7.

Then, write down the leftmost digit, 4.

So, 436×11 = is 4796.

Let’s do another example: 3254×11.

The answer comes from these sums and edge numbers: (3)(3+2)(2+5)(5+4)(4) = 35794.

One more example, this one involving carrying: 4657×11.

Write down the sums and edge numbers: (4)(4+6)(6+5)(5+7)(7).

Going from right to left we write down 7.

Then we notice that 5+7=12.

So we write down 2 and carry the 1.

6+5 = 11, plus the 1 we carried = 12.

So, we write down the 2 and carry the 1.

4+6 = 10, plus the 1 we carried = 11.

So, we write down the 1 and carry the 1.

To the leftmost digit, 4, we add the 1 we carried.

So, 4657×11 = 51227 .

3. Multiplying by 5, 25, or 125

Multiplying by 5 is just multiplying by 10 and then dividing by 2. Note: To multiply by 10 just add a 0 to the end of the number.

12×5 = (12×10)/2 = 120/2 = 60.

Another example: 64×5 = 640/2 = 320.

And, 4286×5 = 42860/2 = 21430.

To multiply by 25 you multiply by 100 (just add two 0’s to the end of the number) then divide by 4, since 100 = 25×4. Note: to divide by 4 your can just divide by 2 twice, since 2×2 = 4.

64×25 = 6400/4 = 3200/2 = 1600.

58×25 = 5800/4 = 2900/2 = 1450.

To multiply by 125, you multipy by 1000 then divide by 8 since 8×125 = 1000. Notice that 8 = 2×2x2. So, to divide by 1000 add three 0’s to the number and divide by 2 three times.

32×125 = 32000/8 = 16000/4 = 8000/2 = 4000.

48×125 = 48000/8 = 24000/4 = 12000/2 = 6000.

4. Multiplying together two numbers that differ by a small even number

This trick only works if you’ve memorized or can quickly calculate the squares of numbers. If you’re able to memorize some squares and use the tricks described later for some kinds of numbers you’ll be able to quickly multiply together many pairs of numbers that differ by 2, or 4, or 6.

Let’s say you want to calculate 12×14.

When two numbers differ by two their product is always the square of the number in between them minus 1.

12×14 = (13×13)-1 = 168.

16×18 = (17×17)-1 = 288.

99×101 = (100×100)-1 = 10000-1 = 9999

If two numbers differ by 4 then their product is the square of the number in the middle (the average of the two numbers) minus 4.

11×15 = (13×13)-4 = 169-4 = 165.

13×17 = (15×15)-4 = 225-4 = 221.

If the two numbers differ by 6 then their product is the square of their average minus 9.

12×18 = (15×15)-9 = 216.

17×23 = (20×20)-9 = 391.

5. Squaring 2-digit numbers that end in 5

If a number ends in 5 then its square always ends in 25. To get the rest of the product take the left digit and multiply it by one more than itself.

35×35 ends in 25. We get the rest of the product by multiplying 3 by one more than 3. So, 3×4 = 12 and that’s the rest of the product. Thus, 35×35 = 1225.

To calculate 65×65, notice that 6×7 = 42 and write down 4225 as the answer.

85×85: Calculate 8×9 = 72 and write down 7225.

6. Multiplying together 2-digit numbers where the first digits are the same and the last digits sum to 10

Let’s say you want to multiply 42 by 48. You notice that the first digit is 4 in both cases. You also notice that the other digits, 2 and 8, sum to 10. You can then use this trick: multiply the first digit by one more than itself to get the first part of the answer and multiply the last digits together to get the second (right) part of the answer.

An illustration is in order:

To calculate 42×48: Multiply 4 by 4+1. So, 4×5 = 20. Write down 20.

Multiply together the last digits: 2×8 = 16. Write down 16.

The product of 42 and 48 is thus 2016.

Notice that for this particular example you could also have noticed that 42 and 48 differ by 6 and have applied technique number 4.

Another example: 64×66. 6×7 = 42. 4×6 = 24. The product is 4224.

A final example: 86×84. 8×9 = 72. 6×4 = 24. The product is 7224

7. Squaring other 2-digit numbers

Let’s say you want to square 58. Square each digit and write a partial answer. 5×5 = 25. 8×8 = 64. Write down 2564 to start. Then, multiply the two digits of the number you’re squaring together, 5×8=40.

Double this product: 40×2=80, then add a 0 to it, getting 800.

Add 800 to 2564 to get 3364.

This is pretty complicated so let’s do more examples.

32×32. The first part of the answer comes from squaring 3 and 2.

3×3=9. 2×2 = 4. Write down 0904. Notice the extra zeros. It’s important that every square in the partial product have two digits.

Multiply the digits, 2 and 3, together and double the whole thing. 2×3x2 = 12.

Add a zero to get 120. Add 120 to the partial product, 0904, and we get 1024.

56×56. The partial product comes from 5×5 and 6×6. Write down 2536.

5×6x2 = 60. Add a zero to get 600.

56×56 = 2536+600 = 3136.

One more example: 67×67. Write down 3649 as the partial product.

6×7x2 = 42×2 = 84. Add a zero to get 840.

67×67=3649+840 = 4489.

8. Multiplying by doubling and halving

There are cases when you’re multiplying two numbers together and one of the numbers is even. In this case you can divide that number by two and multiply the other number by 2. You can do this over and over until you get to multiplication this is easy for you to do.

Let’s say you want to multiply 14 by 16. You can do this:

14×16 = 28×8 = 56×4 = 112×2 = 224.

Another example: 12×15 = 6×30 = 6×3 with a 0 at the end so it’s 180.

48×17 = 24×34 = 12×68 = 6×136 = 3×272 = 816. (Being able to calculate that 3×27 = 81 in your head is very helpful for this problem.)

9. Multiplying by a power of 2

To multiply a number by 2, 4, 8, 16, 32, or some other power of 2 just keep doubling the product as many times as necessary. If you want to multiply by 16 then double the number 4 times since 16 = 2×2x2×2.

15×16: 15×2 = 30. 30×2 = 60. 60×2 = 120. 120×2 = 240.
23×8: 23×2 = 46. 46×2 = 92. 92×2 = 184.
54×8: 54×2 = 108. 108×2 = 216. 216×2 = 432.

Practice these tricks and you’ll get good at solving many different kinds of arithmetic problems in your head, or at least quickly on paper. Half the fun is identifying which trick to use. Sometimes more than one trick will apply and you’ll get to choose which one is easiest for a particular problem.

Multiplication can be a great sport! Enjoy.

See Math tricks on video at the Wild About Math! mathcasts page.

Check out these related articles:

If you enjoyed this post, make sure you subscribe to my RSS feed!

109 Responses to “Impress your friends with mental Math tricks”
By Alex Kay on Nov 19, 2007 | Reply

Hey there!
Just wanted to stop by and say thanks for a great post and read - math doesn’t have to be boring!

Have a nice day,
Alex
By Sol on Nov 19, 2007 | Reply

Alex,

You’re quite welcome. Glad you liked it.

Sol
By Karen (Karooch from Scraps of Mind) on Nov 19, 2007 | Reply

Hey Sol i don’t expect to be using them to impress anybody, but some of those techniques will come in very handy. Thanks a lot. I’ll give it a Stumble so others can learn them too.
By Sol on Nov 19, 2007 | Reply

Karen,

Thanks for the kind words and the stumbling.

Sol
By DJ in Houston on Nov 19, 2007 | Reply

WOW!!!

I wish I knew this while I was in school!!!

That is neat…
By Alan on Nov 21, 2007 | Reply

Very cool - I plan to use this as often as possible. By the way there is a minor typo…
“So, 46×99 = 4600x(100-1) = 4600-46 = 4554.” should read “So, 46×99 = 46x(100-1) = 4600-46 = 4554.”

that’s ok though - this page is so cool i think i’ll let this one slide.
By Sol on Nov 21, 2007 | Reply

Alan,

I’m glad you like the page. I’m not seeing the error, though. Your correction looks to me the same as what I wrote. Please elaborate.

Thanks.
By emily on Nov 22, 2007 | Reply

mental math tricks helps to perform arithmetic calculations quickly
Mental math
By IB a Math Teacher on Nov 22, 2007 | Reply

Multiplying by 11 is easier when adjusting the rule for multiplying by 9. Just think of 11 as (10+1)

So 436 × 11 = 4360 + 436 = 4796…that’s the simpler way of explaining why the digits add up to each other like you wrote:

4360
+ 436
—–
4796
By BPM on Nov 23, 2007 | Reply

Excellent Stumble. Thumb Up.
By Sol on Nov 23, 2007 | Reply

@DJ, BPM — Thanks for your kind comments.

@IB - yes, your way of showing why this “adding the pair” approach for multiplying by 11 is right on.
By Fred on Nov 23, 2007 | Reply

You are saying 46×99 = 4600x(100-1) when it should be 46 instead of 4600.
By Sol on Nov 23, 2007 | Reply

Fred, Alan:

Thanks for the correction. Now I see it!
Article is now fixed.
By encoded on Nov 23, 2007 | Reply

These are just retarded, any idiot could think them up…
By rob on Nov 23, 2007 | Reply

omg the trick for multiplying squares is awesome.

-Rob
By Sol on Nov 23, 2007 | Reply

Rob,

Glad you liked it.
By Shao Han on Nov 25, 2007 | Reply

Even primary school students know these simple tricks in China…..
By Sol on Nov 25, 2007 | Reply

Shao Han,

Can you recommend any books in English where I could learn about what Math Chinese students learn?
By BlueS on Nov 26, 2007 | Reply

Hi, I has got a problem with multipling:
If i multiply some numbers in that metod some things go wrong:
E.G. (agree):
87 * 81
88*80 + 7 = 7047

38*20
38*20 + 0 = 760

E.G.(doesnt agree):
56 * 17
63*10 + 42 =’ 672
Real: 952

75 * 88
93*70 + 40 =’ 6550
Real:6000

85 * 26
91*20+30 =’ 1850
Real: 2210

Please tell me what mistake was doing!
By Sol on Nov 26, 2007 | Reply

Hi BlueS,

I assume you’re trying to use technique #4 in the article. That technique only works when the two numbers differ by a small even amount and when you can easily calculate the square of the number in the middle of the two numbers (i.e. the average).

In your example of 56×17 I see what you’re trying to do but it’s different than this trick.

Let’s look at your example:

Let a=56
Let b=17

You want to calculate a*b, right?

I see that you added 7 to 56 and subtracted 7 from 17 so that you could multiply by 10. That’s a good idea.

So, you were computing (a+7)x(b-7).
(a+7)x(b-7) =
(axb)-(7xa)+(7xb)-49 =
(axb)-7x(a-b)-49

So, (axb) = (a+7)x(b-7) + 7x(a-b)+49

Or, 56×17 = 63×10 + 7x(39)+49 = 630 + 273 + 49
= 952

This approach is not easy for these two numbers.

What you could do with what you’ve noticed is to say that 56×17 = 56x(10+7) = 56×10 + 56×7
= 560+392 = 952.

Does this help?
By Alex on Nov 26, 2007 | Reply

everyone should already know this in my opinion. it’s basic basic math.
By Amanda on Nov 26, 2007 | Reply

I agree that everyone should know things like how to multiply by 9 or 11. However, the method used to achieve the answer may be quite different. I was taught multiplication and agree that it is basic math, however I was never taught “tricks” such as this; basically easy ways to remember how to multiply certain numbers. I am horrible with math so ordinarily I cannot do multiplication in my head. However, with these tips, I may get better at it.
By Sol on Nov 26, 2007 | Reply

@Alex: Knowing these tricks is largely about having a relationship with numbers. I’m glad you have it but not everyone does.

@Amanda: Do report back on how these techniques help you if they do. The Vedic Math approach allows people to do multiplication without knowing more than up to 5×5 in their multiplication tables. I’ll post some Vedic Math techniques in the future.
By wheyyyy on Nov 26, 2007 | Reply

good tricks mate. you make it easier. nice one.

dont listen to them < >.
By Grinch on Nov 27, 2007 | Reply

Your annotation for the multiplying by 9’s is wrong. You have:

9×9 is just 9x(10-1) which is 9×10-9 which is 90-9 or 81

If you follow the acronym PEMDAS you would do what is in the parenthesis first and then multiply which would give you 9×9. You should have stated you need to use the distributive method. Which would mean it would read (9×10)-(9×1)= 90-9= 81.
By E! on Nov 28, 2007 | Reply

This is a great system developed a long time ago by Jakow Trachtenberg whilst in a Nazi camp. More info here; http://en.wikipedia.org/wiki/Trachtenberg_system
By EPIc on Nov 30, 2007 | Reply

there is an easier way to multiply by 9.

this is the way I learned when i was in school.

this works all the way up to 9 x 9, but if you’re in elementary school, it can come in handy.

take the number you are multiplying 9 by, and subtract one. then figure out what number plus that number equals nine.

put the first and second answer beside each other and you get tour answer.

it’s simpler than it sounds…..
example:
9 x 7 = ?
7 - 1 = 6
6 + 3 = 9
the answer is 63!

9 x 3 = ?
3 - 1 = 2
2 + 7 = 9
the answer is 27!

this was the easiest way for me.
By Ragesh on Dec 2, 2007 | Reply

Well let me put the technique #4. Generically it uses the fact that (a+b)*(a-b) = a^2 - b^2. Here b is half of the difference between the numbers, hence a is the average. In the example where difference is 6, the minus 9 comes coz (6/2)^2 = 9. Similary it can be done for large differences also, but it depends how comfortable is one is with squaring numbers.
By Jon Gjengset on Dec 2, 2007 | Reply

I love this!
There is one problem with technique #6 though:
Take 81*89 where the first digits are equal, and where the last digits’ sum is 10.
By applying your method the answer should be: (8*9)(9*1) which gives 729, when the correct answer is 7209. This happens in all cases where the product of the last digits is less than 10 (ie with 9 and 1), so a quick fix would be to always make sure you have two digits in the product, and if not then add a zero in front.
By Jon Gjengset on Dec 2, 2007 | Reply

Oh!
I just dicovered that the problem I mentioned above also applies to technique #7!
If the square of the second number is less than 10, you also have to add a zero before it in order to get the right answer:
Wrong:
92^2
=> 180 =>360
814
360
1174
Right:
92^2
=> 180 => 360
8104
360
8464
By Pick Up Artist 4 Life on Dec 3, 2007 | Reply

This is great for “impressing” the somewhat math smart girls. I’m sure that the math wizzes already know this.

Bookmarked

Adam

===
http://www.BecomingAPUA.com - V is the #1 Pick Up Artist
===
By Jezz on Dec 4, 2007 | Reply

I invited #8 a long time ago… at least, I thought I did. LOL
By yusuf on Dec 4, 2007 | Reply

very nice math trick.. wish i had known when i was in school.. if you ask me, i would suggest to put them in elementary school’s curriculum
By Neil on Dec 4, 2007 | Reply

Great work, very useful.
By Gemeda on Dec 4, 2007 | Reply

A fantastic work! I didn’t just like it, I loved it. I have so much respect and appreciation for people like you who spend their time doing something productive on the net.

Thanks man!
By Nature Wallpaper on Dec 4, 2007 | Reply

finally :)!!
By josh on Dec 4, 2007 | Reply

have never been good with numbers, but these things do help quite a bit. how come we were never taught this at school???
By Varun on Dec 4, 2007 | Reply

Anyone who has taken CAT exam in India know all these techniques and more.
By The Queen's English on Dec 4, 2007 | Reply

:%s/math/maths/g
By THE CHEAPEST FLIGHT FINDER on Dec 4, 2007 | Reply

Great post! Good tricks for life.
By max on Dec 4, 2007 | Reply

amazing tricks!
By devin on Dec 4, 2007 | Reply

heres a real trick

(a+b)^2 = 2a^2 + 2ab + b^2, so

86^2 = (80+6)^2 = 80^2 + 2*80*6 + 6^2

so 80^2 is easy 8^2+10^=6400
2*80*6=2*10*6*8=2*480=960
6^2 = 36
add

=7396

works for any number 0-99 pretty easily
By Virtaaj on Dec 4, 2007 | Reply

@Varun: True.. very true!
By naomi on Dec 5, 2007 | Reply

@ EPIc

my little brother when he was 7 taught me (age 21) the easiest way to multiply by 9 (only works up to 9×9):

Hold your ten fingers out in front of you. Now let’s say we multiply 9×3.

Starting from your left pinkie, count three fingers (end up at your left middle finger). Fold it down. Now read your fingers. 2 (fold) 7. 27.

Try 9×6. Count from left pinkie, end up at right thumb. Fold down. Read… five fingers, fold, four fingers. 54.

EASY!

And to all of you from China, India, etc, it’s great that your primary schools taught math tricks. But many (most?) in America do not, and your comments are not constructive, almost hurtful. I go to MIT yet I still can’t do basic arithmitic in my head. Don’t belittle people because they want to learn- it’s never too late to learn!
By AHmed on Dec 5, 2007 | Reply

cool
By Zoe on Dec 5, 2007 | Reply

@ naomi

You’re not quite right about that finger trick- I use it too, and it can be easily adapted to 9×10-9×20 (it works higher than this too but takes some playing around, and not all numbers work out perfectly- I’ll let you try that!)

ie 9×13

Do the same thing for 9×3 as naomi says. Except now your leftmost pinkie is 100. Read left to right- 1 finger (100), 1 finger (10), fold, seven fingers. Answer = 117.

9×16 therefore would be left pinkie (100), four, fold, four. 144.
By Stock Broker on Dec 6, 2007 | Reply

Boy this was cool one. Simply splendid.After reading this my maths seem to have improved
By gmac refinancing a home with no money on Dec 6, 2007 | Reply

Hi My wife and I would like to thank you all for this web site. Hours of pleasure and all
By bill weaver on Dec 6, 2007 | Reply

BlueS, Sol -

For 56×17, the 2x rule seems easier here. 2×2x2×7 = 56, so do 7×17, then x2 three times.

7×17 = 119 (7×10 + 7×7)
x2 = 238
x2 = 476
x2 = 952

Great article, Sol. Lots of fun.
By Chris on Dec 6, 2007 | Reply

Regarding #2. A similar trick works for multiplications with 111, 1111, … you just need to make the “pipeline” longer.

Example:
24253 * 111 = (2) (2+4) (2+4+2) (4+2+5) (2+5+3) (5+3) (3) = (2) (6) (8) (11) (10) (8) (3) = 2692083

It works for 101, 1001 too, where you need to “skip” a position or two when adding. Example:
24253 * 101 = (2) (4) (2+2) (4+5) (2+3) (5) (3) = 2449553
By Yakeen on Dec 7, 2007 | Reply

I will probably need some more help on this.
By Mathletics..huhu.. on Dec 8, 2007 | Reply

sounds fun to me…math is really great.my fav subject wat??!!??
By shivashis on Dec 8, 2007 | Reply

Boy, all the posts are just great.
By Dale on Dec 9, 2007 | Reply

Some trippy stuff, but still cant remember it

http://dzrbenson.com/blog/
By Jonathan on Dec 9, 2007 | Reply

Somehow I missed this post! I use some of these, and in combination with other tricks. And I share some with students.

Fun stuff!
By abiel_marlon on Dec 10, 2007 | Reply

that was a nice trick hu! have another trics there?
By kerato on Dec 10, 2007 | Reply

Here are some more
By sahil on Dec 11, 2007 | Reply

@ naomi

its a common myth in india, that indians are much better in mathematics than, especially, americans … only after coming to america did i realize how untrue this is!

Though Varun may be better in speed mathematis than all of us, the same can not be extrapolated for all indians.
By shestheoneforme on Dec 16, 2007 | Reply

Neat! I like things like this, that encourage you to go beyond the basics we all learned from the very beginning!
Simple logical things like 57 * 9 = 57 * 10 - 57 seem so obvious once you see them, but you need to take that step!
By Lara on Dec 17, 2007 | Reply

A trick for multiples of 9 that I learned was to hold out your hands and bend down the number you wanted to know about.

Example:

What is the result of 5 * 9?

You bend down the fifth finger on your left hand, resulting in 4 fingers left before the bend, and 5 fingers left after the bend, equals 45.
By Sol on Dec 17, 2007 | Reply

Hi Lara,

Yes, that’s a nice technique for multiplying single digits by 9. It’s a nice way for children to use their kinesthetic senses to start learning arithmetic.
By Kannan.M on Jan 8, 2008 | Reply

Very usefull
Thank you
By aaron on Jan 10, 2008 | Reply

i always use the 9′trick it’s easy
By rei on Jan 13, 2008 | Reply

Coool tricks!! these will come handy in real sitautions
By rei on Jan 13, 2008 | Reply

To be frank

Some of these tricks are also taught in Bangladesh at a very tender age….which we dont really recall when grown up….few tricks are published in a 5 grader book…

Nevertheless its a great effort though…
By amber on Jan 13, 2008 | Reply

these are some cool tricks
By Sol on Jan 14, 2008 | Reply

@Kannan, Aaron, Rei, Amber: I’m glad you like these tricks.
By Jolo on Feb 7, 2008 | Reply

Hi there

just wanted to say that your mental math tricks are magnificent. Their all useful, Thank You.
I am hoping you could post more math techniques
By graphed on Feb 9, 2008 | Reply

wow, what a strange math! LOL!
By Sol on Feb 10, 2008 | Reply

Jolo,

I’m glad you like these tricks. Yes, I’ll post more over time.
By Matematik Özel Ders on Feb 26, 2008 | Reply

thx
By Airedale on Feb 28, 2008 | Reply

Perhaps you can decipher a trick on another blog http://web.missouri.edu/~woodph/html/mult_200_300_etc_.html

He discusses multiplying,for ex.
204 x 208= (2×2)(4×8x2)(4×8). My problem is that 4×8x2=64 but the answer to the problem is 42432. 24
By Airedale on Feb 28, 2008 | Reply

24 does not equal 64
By Airedale on Mar 3, 2008 | Reply

so my question is, does that trick work for numbers other than squares?
By celestine Umunnakwe on Mar 5, 2008 | Reply

I am not good at maths but I am very interested in knowing how to solve mathematical problems. Your site have been a very helpful tool to me. I will appreciate it if more mathematics tutorial are made available, especially on how to divide numbers quickly.

I like this site.

thanks
By Burton MacKenZie on Mar 30, 2008 | Reply

Nice list, some I didn’t know. Here’s one not on your list for squaring a number - http://www.burtonmackenzie.com/2008/03/more-math-in-head.html
By Carlos Gomez on Apr 1, 2008 | Reply

como se multiplica 93 por345
By abhinav on Apr 14, 2008 | Reply

this tricks are very useful for a primary student.
By yomanyo on Apr 15, 2008 | Reply

its very common plz.insert some better trick for both junior and senir standard.
By mitchelle on Apr 16, 2008 | Reply

i love this it helped me alot
By mohamed fakhry on Apr 17, 2008 | Reply

this page very useful and thank you for this information
By Lori on Apr 23, 2008 | Reply

—Airedale I think it’s a typo or something. Cause to get the middle # u add the 3rd digit #s (in that case was 8+4). then multiply by the first digit # (which was 2) I did the example you gave plus another one. Hope it helps.

In this problem you would do the
2*2=4
(4+8)*2=(12)*2=24
4*8=32
Then the answer would be 42432

Another example 209*203
2*2=4
(9+3)*2=(12)*2=24
9*3=27
Then the answer would be 42427

Another one 207*206
2*2=4
(6+7)*2=(13)*2=26
6*7=42
So answer would be 42642
By Roma on Apr 23, 2008 | Reply

this site is great! The post and some of the comments are very useful. I’ll be needing this soon in training the kids in our school in math. thanks so much!
By sophobic on Apr 26, 2008 | Reply

*im from the philppines
*thanks for this
*well done ^_^
By billy bob joe on Apr 28, 2008 | Reply

These tings are weird….
By billy bob joe on Apr 28, 2008 | Reply

These things are REALLY weird…….
By anna lou on Apr 28, 2008 | Reply

wow its great!!!!!!!! i learned different tricks in solving math problems.
By John Morrison on Apr 29, 2008 | Reply

I have a good way to do 9 tables and multiplications. Think of 9 in this way. Subtract one from the first number and place the difference between it and 9 on the end. 2×9 is 1 and 8 or 18. 3×9 is 2 and 7 or 27. 4×9 is 3 and 6 or 36. Do you see the pattern?
By k.kaushik on May 1, 2008 | Reply

multypling numbers by 11

ex;54*11=594
54=5+4=9
at middle 9 left side 5 and right side 4
thanking you
By k.kaushik on May 2, 2008 | Reply

Multiplying by 11, Simple trick

ex:63*11=693

Take 63 add the digits i.e 6+3=9
now place the result i.e 9 in middle of 63
then we get result as 693.

Hope this trick is useful.

Cheers…:)
Kaushik
By gaurav sinha d.p.s school,patna on May 15, 2008 | Reply

it has really elped me . now shipra class 9 g allows to suck her moms ass & daddy penis. i am a big mother fucker .
By abhishek bachan on May 15, 2008 | Reply

thanku . due to this i can fuck my ass . chodane waqt mere ko itna maja ata hai ki mat poocho mera to gaar phat jata hai yaar