basic mathematics image
 basic mathematics image

Multiplication by 11


To understand the multiplication by 11 trick, take a look at the following multiplication below:


Multiplication-by-11-image




Did you make the following two important observations?

First, notice that the digits of the number that is multiplied by 11 appear again in the answer

Second, the number in the middle of the answer is always found by adding the digits of the number that is multiplied by 11

This is the basic facts that you have to remember to quickly multiply numbers by 11

Therefore, if you want to use this trick, all you have to do is add the digits of the number and put the answer between the number

Other examples

1) 35 × 11

Just add 3 and 5 to get 8

Put 8 between 3 and 5

The answer is 385

2) 18 × 11

Just add 1 and 8 to get 9

Put 9 between 1 and 8

The answer is 198

3) 43 × 11

Just add 4 and 3 to get 7

Put 7 between 4 and 3

The answer is 473


Now, look at this example 48 × 11
Add 4 and 8 to get 12

Just put 12 between 4 and 8???

No, it does not work like this!

You can still put 2 in between. However, since the number is bigger than 9, you have to carry the 10 represented with a 1 over the 4

1 + 4 = 5. Thus the answer is 528

4) 85 × 11

Just add 8 and 5 to get 13

Add 1 to 8 to get 9

Put 3 between 9 and 5

The answer is 935


5) 78 × 11

Just add 7 and 8 to get 15

Add 1 to 7 to get 8

Put 5 between 8 and 8

The answer is 858






Page copy protected against web site content infringement by Copyscape





worksheets-banner










Copyright © 2008-2015. Basic-mathematics.com. All right reserved

Are you a fan of this site? Support us     Our awards!     Our partners     About me     Disclaimer     Build your website!     Advertise on my site
    Try our free toolbar     Like us on Facebook     Take our survey     Illustrated fractions     Educational math software     Math jobs     Best Teacher Sites Now     Teachers/Students tools     Search math jobs     Algebra ebook     Fraction ebook     Geometric formulas ebook