Maths Fun » The Miracle of 11
Do you know there’s a great trick to multiply by 11? Obviously single digit numbers multiplied by 11 are easy but it appears to get much more difficult when there are double-digit numbers that are multiplied by 11. When you know the secret to multiply any two-digit number by 11, you will be able to astonish your friends and teachers. (There may even be some teachers that don’t know the trick that you’ll learn in this lesson!). 11 multiplication is very easy when you know these simple trick and it will make you look like a mathematical wizard.
Do you want to learn the fun and easy way to multiply any two-digit number by 11? Here is what you need to do, given that the sum of the digits when added up does not exceed 10.
For example, you want to multiply 11 by 45. The first thing you need to do is add both numbers – the answer will be 9. Put the answer in between the two digits, so 495. That is the answer to the equation 11 by 45.
What if the digits, when added up, are more than 10? Here is what you need to do.
For example, the number is 58. Add 5 and 8 – the answer will be 13. Add 1 to the first digit (5 – to make it 6) and place the number 3 in between 5 and 8. The answer to the equation 58 x 11 will be 638.
This method is also applicable for big numbers that have to be multiplied with the number 11. For example, you need to multiply 12345432 with 11.
Place the two number ones at the start and the end of your number. Start at the right as you add each digit with the digit on its left. For this number, you have to add 1 with 2. Make three your second digit (after the number 1.) Add 2 and 3 and put your answer (the number 5) as the third digit. The fourth digit should be 7 (3+4), the fifth should be 9 (4+5), the seventh should be 7 (4+3), the eighth should be 5 (3+2) and the ninth should be 3 (2+1.)
The answer should be 1357997531 for the equation 12345432 x 11.