# Quick Multiplication up to 20 x 20

“I’m having trouble above 10×10.”

This was a statement I heard many times while interacting with students preparing for competitive examinations including CAT. This was in response to my appeal to them to memorize tables up to 20×20.

Today I am posting here on QuickerMaths.com, the method which I recommend to my students too.

How to multiply up to 20×20 in your head?

Assumption: You know your multiplication table reasonably well up to 10×10.

I am trying to explain this with an example,

Say you want to multiply – 16 x 13

Step 1 – Add the unit’s digit of one to the other number –

Here, add 16 + 3 = 19

Or, add 13 + 6 = 19

Step 2 – Put a zero after the number (i.e. multiply it by 10)

Here, 19 becomes 190

Step 3 – Multiply unit’s digit of both the numbers

Here, 6×3 = 18

Step 4 – Add the product to the result of Step 2

Here, 190 + 18 = 208

Simple!! Isn’t it?

Another example, 17×19 =  (17+9)*10 + (7*9)  = 260 + 63 = 323

(10+a) * (10+b) = 100 + 10b + 10a + a*b
= (10+a+b) * 10 + a*b
==========
This can be extended to sums like 23 * 28
(20+a) * (20+b) = 400 + 20b + 20a + a*b
= (20+a+b) * 20 + a*b
So, 23*28 = (23+8)*20 + 3*8 = 620 + 24 = 644.
==========
& so on.

by NANDEESH H N

Try for yourself. Let me know (by posting a comment below) if you liked it.

Click here for some more fast multiplication tricks

## 34 thoughts to “Quick Multiplication up to 20 x 20”

1. ANAND P says:

I HAD A DOUBT IN THE CASE OF 20*17 AND 13*20…….? DIGIT VALUE ZERO CASE!

2. nikita says:

Thanks vineet 🙂

3. nidhi says:

hey,is it any specific books available 4 this???????????????????????
plz tell,i need it…………………………………

4. rani says:

its very nice n useful

5. Niranjan Bhandi says:

Hi Nandeesh

can you tell me the above formula can be used in any two digit multiplication

and for three digit multiply what is the formula for ex: 839478*625

waht are short cut tricks for square, cube root, Division

6. varsha upadhyay says:

THANKS!!! FOR THE GREAT TRICKS!

7. khalid says:

another trick which suits to all two digit multiplication is
Eg-25*24
(5*4) multiplying one’s(here we remains with carry 2 ie 5*4=20)….0
now multiplying criss cross (5*2)+(4*2)+carry ie 2 is 20…..0
now multiply ten’s (2*2)+carry ie 2 is….. 6
the ans is 600

1. nikita says:

thanks khalid 🙂

2. nikita says:

how does it work for 3 digit numbers?

8. Sai says:

great job yaar…

9. Sundeep says:

Thumbs up to Sanjay Patel… His method works for any 2 digit and 3 digit numbers multiplication of anytype.. Thanks a lot..

10. p k swain says:

absolutely amazing like that of serving on someone’s plate to fill one’s hunger. thanks.

11. Rajeev Nair says:

Very nice and helpful. definitely stimulates one’s intellectual faculties.

12. ray an arcane says:

great things r there…………ray

13. ???? ???? says:

??? ???? ?? ???????? ?? ????
235 *142=?
2 3 5
1 4 2
_____
????=5*2=10=0
1 ?????
????=?. ?? ?. ?? ???? ?? ?????? ???? ?? ???
=3*2 + 5*4=6+20=26
????? ?? ????=26+1=27=7 ,????? 2

?????=2*2 + 5*1 + 3*4
=21=????? ????=23=3, ??.=2

????=2*4 + 3*1=11+??.2=13=3, ??.1

???=2*1=2+??.1=3

????? ??? ???. ??. ?. ?
3 3 3 7 0
??? ??? ???…

1. Vineet Patawari says:

Sanjay Patelji thanks a lot. This is the criss-cross method of vedic maths…i’ll soon post an article on the same!!

2. RAJEEV MAHADANI says:

Dear, is there any another short cut then Matrix?

14. ???? says:

??

15. Deepika says:

thanks
sir

16. vaijanath patil says:

thank you very much nandish

17. zloben says:

I would like to exchange links with your site http://www.quickermaths.com
Is this possible?

18. James Boehne says:

I almost certainly would not have contemplated this was valuable two or three years ago, yet it’s fascinating how age evolves the manner you respond to things, many thanks for the article it really is great to discover something smart now instead of the typical rubbish masquerading as blogs and forums over the internet. Regards

19. NANDEESH H N says:

13*18 = (13+8)*10+3*8 = 234
23*28 = (23+8)*20+3*8 = 644
33*38 = (33+8)*30+3*8 = 1254
43*48 = (43+8)*40+3*8 = 2064
53*58 = (53+8)*50+3*8 = 3074

1. Deepika says:

thanx NANDEESH H N
these tricks r really awesome
hy can u tell me D shortcut trick of multiplying 45*487
thanx

1. NANDEESH H N says:

Same shortcut does not work everywhere.

One way of solving your problem is:
45*487 = 90*487/2 = 43830/2 = 21915

2. Anupam Das says:

another approach:
hy can u tell me D shortcut trick of multiplying 45*487

45*487=(50-5)*487=(487*50)-(487*5)= (487*100/2) – (no need to calculate it now)
= 24350-2435=21915…just trying it, in this way nos can be calculated mentally ofcourse with practice

2. Rudrasai says:

Hi Nandeesh,

Can u tell me short trick for 76*45
Bcoz above the nos are in 10’s or 20’s or 30’s.

Thank you

1. Anupam Das says:

76*45= simple use the guys method of criss-cross as explained in hindi.

or u can use 76*(50-5)=its very easy to multiply by 5 ain’t it

=(76*100)/2- no need to calculate it now= 3800-380=3420…ans

3. Vilas Thakur says:

13 *18 = 1*( 13 + 8 ) l ( 3 * 8 ) = 1*21 l 24 =21 l 24 = 234
23 *28 = 2*( 23 + 8 ) l ( 3 * 8 ) = 2 *31 l 24 = 62 l 24 = 644
33 *38 = 3*( 33 + 8 ) l ( 3 * 8 ) = 3 *41 l 24 = 123 l 24 = 1254
43 *38 = 4*( 43 +8 ) l ( 3 * 8 ) = 4 *51 l 24 = 204 l 24 = 2064
53 *58 = 5*( 53 + 8 ) l ( 3* 8 ) = 5 * 61 l 24 = 305 l 24 = 3074

20. keshav says:

i want multiply up to 50*50

21. lovely says:

ahm ang hirap naman po.paano kung 63×17??ganyan po din ba na steps ang gagamitin???

22. MAHI says:

THIS IS TOO MUCH TIME WASTE METHODS ………….

23. NANDEESH H N says:

Very good!
(10+a) * (10+b) = 100 + 10b + 10a + a*b
= (10+a+b) * 10 + a*b
==========
This can be extended to sums like 23 * 28
(20+a) * (20+b) = 400 + 20b + 20a + a*b
= (20+a+b) * 20 + a*b

So, 23*28 = (23+8)*20 + 3*8 = 620 + 24 = 644.
==========
& so on.

1. Vineet Patawari says:

Thanks Nandeesh!!

I have included your comment in the post itself.

Really glad that people like you visit this blog and contribute for everyone’s benefit. Thanks again!