We all know that it is easy to multiply a single digit number by 11. If you want to multiply 4 by 11, you simply repeat the digit for the answer, 44. If you multiply 6 by 11, you get 66.
Did you know it is easy to multiply two digit number by 11?
Multiplying a two-digit number by 11.
To multiply 16 by 11, add both the digits of the given number, 1+6 = 7. Now place this answer , 7, in between the two digits, in this case giving you 176.
16 X 11 = 176
These calculations are easy to do in your head. If somebody asks you to multiply 52 by 11, you could immediately say, "five hundred and seventy two".
That was easy! Now, what happens if the digits add to ten or more? It is not difficult - you simply carry the one (tens digit) to the first digit. For example, if you were multiplying 78 by 11, you would add 7+8=15.
Put the 5 between the digits and add the 1 to the 7 to get 858.
Let's try another example. To multiply 95 by 11.
9+5 = 14
Now carry 1 over 9.
1 plus 9 gives you 10. We work with 10 the same way as we would with the single digit number. Ten is the first part of our answer, 4 is the middle digit and 5 remains the final digit.
So, 95 X 11 = 1045
This approach also applies to numbers such as 22 and 33. Twenty-two is 2 times 11.
To multiply 17 by 22, you would multiply 17 by 2 to get 34.
Now 3+4 = 7.
Using the shortcut that we have learned, place 7 between the 3 and 4.
We get, 374
We see, 17X22 = 374
Practice some problems for yourself and you will be surprised how fast you can call out the answer.
