Multiplication of any number with 11 in a second

Technique to multiply 11 with any number within a second

Let me start with an example to illustrate you. We will multiply 11 with 635 i.e. (11*635).
So, let us start.
First write 635 like this:
               6
               3
               5
Now at first step write the last digit as it is.
Here we write 5 as last digit is 5.
Now at second step we add the last two numbers as: (5+3=8).
Now at third step we add (6+3=9).
And finally we write the first digit as it is i.e. 6
So, the final answer is 6985.

This is how we do.
Now let us do some other examples so that it makes us easier in solving problems.
Example:1
712642*11 
1. Write last digit i.e. 2
2. Now add (4+2)=6
3. Again add (6+4)=10.
            NOTE: So, here comes the problem. In this case write the last digit of 10 i.e. 0 and let 1 
                         to be carried over.
 So, in 3rd step write only 0
4. Now add (2+6)=8,
    BUT we have 1 left as carry over in 3rd step.
    So, we add 8 with 1 (8+1)=9
5. Similarly, we add (1+2)=3.
6.  Similarly, we add (7+1)=8.
7. Finally we write the first digit  7 as it is.
So, our answer will be 7839062.

Example: 2
2084*11
1.                    4
2.          8+4=12. (But we write only 2 and let 1 to add in coming process)
3.           0+8=8. (So we add last digit 8 with 1, so the final answer will be 9)
4.           2+0=2.
5.                    2
6.   22924  

This will be helpful for you.
Enjoy it.