## How do you multiply any number by eleven mentally?

Explain and give at least 3 examples. Please more than 2 examples with a brief explanation.( Numbers bigger than 25 or 25?
Please more explanations with more details and the definition or steps in how to do it. It is an oral exam so I have to give examples and i have to recite the steps in doing it. Please help. Please. I need examples of numbers multiplied by 11. But they should be more than 2 digits. 3 digits please or any odd number! Or any even number THANK YOU!

To multiply any two digit number by 11:

* For this example we will use 54.
* Separate the two digits in you mind (5_4).
* Notice the hole between them!
* Add the 5 and the 4 together (5 + 4 = 9)
* Put the resulting 9 in the hole 594. That’s it ! 11 × 54 = 594

And if da sum of da two numbers > 9, then simply add da tens digit one step towards da left.

* Lets take 66 as an example
* Seperate the two digits in you mind (6_6).
* Add the two sixes together. (6 + 6 = 12)
* Put da units numbers in da middle, i.e. 2 and add da tens numbet to da left = (726)

Hope this helps
Bye !!
by:
on: 15th August 11

### 10 Responses to “How do you multiply any number by eleven mentally?”

1. Don says:

If you have a two digit number, add the two numbers. If the sum is less than ten, then that is the middle number and the original number is the first and third respectively.

25: 2 + 5 = 7 therefore 275

32: 3 + 2 = 5 therefore 352

If the sum is greater than 9, then you have to carry the extra digit:

48: 4 + 8 = 12 therefore 528

2. VFBundy says:

Add the two digits together (of the number you’re multiplying by 11) and place the result on the inside of the two digits of that number.

Ex.: 34 x 11. 3 + 4 = 7, so put the 7 in the inside of 34 = 374.

Ex.: 58 x 11. 5 + 8 = 13. You put the 3 in the middle of the 5 and 8 BUT since the total is a double-digit number, you “carry the 1″ and change the 5 (in 58) to a 6. So the answer = 638.

Ex. 97 x 11. Same as above where the result is a double-digit number. (9 + 7 = 16.) You put the 6 in the middle of the 9 and 7 and “carry the 1″. But, this time, the 9 increases by 1 to 10. So, the answer is 1067.

———————————————————————————————–

3. J says:

25*11 = 2(2+5) 5 = 275

63*11 = 6 (6+3) 1= 693

125 *11 = 1(2+1) (2+5)5 =1375

92*11 = 9 (9+2) 2 ( 9+2=11> 9, ) , then it is ( 9 +1) 1 2= 1012

4. bskelkar says:

Why numerical examples?
If the digits in the number are abcd i.e. 100a+100b+10c+d then 11xabcd = (abcd0+abcd) that’s all!
325×11 = 3250+325 = 3570. SImple!
78×11 = 780+78 = 858. Got it?

5. Next_Fall says:

Here’s how I do ALOT of multiplication in my head. Think about it like this..
When you multiply, you’re getting so many sets of so many (just think about it like that)
Instead of saying 11 times 15 you can think of it as 15+15+15, etc. I know this is what they said NOT to think of it as but here’s why I say it.

When you multiply any number by 10 you just add a 0 onto the end of it, unless it’s a decimal but we won’t get into that..

So 10×10 = 100
Here’s why this is useful.

11 is just one off of 10. Instead of just taking the bulk of the problem as 11 x (your number), break it down as 10 * (number) + (number)

Here’s an example. 39 * 11. Think of it as 39 * 10. that’s 390. Now you have the 1 39 left over, add it on to get 429.

another example 526 * 11. 526 * 10 = 5260 +526 = 5786.

I hope you understand what I mean. It seems really complicated for how simple it really is

6. benny yao says:

11=10+1
26: 26×11=26×10 +26×1=260+26=286
27: 27×11=27×10+27×1=270+27=297
28: 28×11=28×10+28×1=280+28=308

7. Sparky says:

Multiply the number by 10, then add the original number. This works because …
11 * x
= (10 + 1) * x
= 10*x + x

If you are looking for some mental short cuts, for two digit numbers you can do the following …
1. Let xy be your two digit number that you wish to multiply by 11.
2. x will likely be the first digit of xy * 11.
3. x+y will be the second digit of xy * 11. If x+y is greater than or equal to 10, add 1 to the first digit.
4. y will be the final digit.

Here are some numerical examples:

36 * 11
3, 3+6, 6
396 = 36*11

74 * 11
7, 7+4, 4 (Note 7+4 >= 10, so carry the 1).
814 = 74*11

For 3 digit numbers, there is a similar flow.
xyz * (10 + 1)
= xyz0 + xyz
(x, y, z are single digits that together make a 3 digit number)

Writing the number from right to left (instead of the usual left to right), …
The 1st digit will be z.
The 2nd digit will be y+z
The 3rd digit will be y+x + any carry over from the 2nd digit.
The 4th digith will be x + any carry over from the 3rd digit.
The 5th digit if it exists will be (1) the carry over from the 4th digit.

Hope this helps.

8. Mr. Kurtz says:

I like Don’s approach, but this may be easier to digest.

If x = some number then:

11x = 10x + 1x

Example: 45 x 11

(45 x 10) + 45 = 450 + 45 = 495

or by using distributive property

45 x 11 = 45(10 + 1) = 450 + 45 = 495

Notice that you are simply adding zero the original number (45 becomes 450) + the original number (45) to get the final number, 495.

This also works the other way. Suppose you wanted to multiply 45 by 9?

45 x 9 = 45(10 -1) = 450 – 45 = 415.

9. meplayingpyramids says:

From some quick calculations, here is what I came up with.

If it is a two digit number multiplied by 11, the digit in the “ones” place will be the last digit, the sum of the two digits will be in the “tens” place, and the “tens” digit from the original number will be in the “hundreds” place. Unless, the sum of the original digits is greater than 10, in which case you have to add one to the first (“tens”) number.

Example: 53*11 = 581 or 5(5+3)1. 65*11 = 715 or (6+1)(6+5)5

For a three digit number represented by abc * 11. The answer will be a in the “thousands” place. (a+b) in the “hundreds” place, (b+c) in the “tens” place, and c in the “ones” place. or a(a+b)(b+c)c
Remember to carry if any sum is greater than 10.

Example: 543 * 11 = 5 (5+4) (4+3) 3 or 5973
Example: 555 * 11 = 5 (5+5) (5+5) 5 or 6105 as you have to “carry the 1″.

So, for two digit numbers ab – a (a+b) b
Three digit numbers abc a (a+b) (b+c) c

I hope this helps.

10. Bruce lee says:

To multiply any two digit number by 11:

* For this example we will use 54.
* Separate the two digits in you mind (5_4).
* Notice the hole between them!
* Add the 5 and the 4 together (5 + 4 = 9)
* Put the resulting 9 in the hole 594. That’s it ! 11 × 54 = 594

And if da sum of da two numbers > 9, then simply add da tens digit one step towards da left.

* Lets take 66 as an example
* Seperate the two digits in you mind (6_6).
* Add the two sixes together. (6 + 6 = 12)
* Put da units numbers in da middle, i.e. 2 and add da tens numbet to da left = (726)

Hope this helps
Bye !!