Think of a number between one and 99. Write it down on a piece of paper. Write the number 11 directly beneath it.
Take the top two numbers and add them together. If the sum is less than 10, simply rewrite the top number with the sum of the first two in between them. For example, if you wrote down 36, add 3 and 6 to get 9. Then place the 9 between the 3 and the 6. Your answer is 396. .
Perform an additional step if the top numbers add up to 10 or more. You will then need to carry the one over and add it to the first of the two numbers. For example, if you multiply 89 by 11, you would add 8 and 9 to get 17. Place the 7 in front of the 9 and add the 1 to the 8 to get 9. Your answer would be 979.
Use the calculator to check your work.