In the previous post, we learned a cool math trick on squaring numbers (positive integers) ending in 5. We did not only learn the math trick itself, but we also discussed why it works. In this post, we will explore another math trick which is multiplying 2 digit numbers by 11.
The Copy-Add-Copy Method
To multiply 2 digit numbers by 11, we will use the copy-add-copy method. We will copy and add the digits of the number multiplied by 11. Below are the steps of this method.
Steps in Multiplying 2-Digit Numbers by 11
- Copy the ones digit of the number multiplied by 11 to the ones digit of the product.
- Add the ones digit and the tens digit of the number and copy the sum (see *) to the tens digit of the product.
- Copy the tens digit of the number (see **) to the hundreds digit of the product. Continue reading
, 
, and hypotenuse 
, the following equation holds
.
