Multiplication of decimal numbers

When you need to multiply decimal numbers by a multiple of 10 (e.g. 10, 100 and 1 000), do not just “move the comma”. First you have to understand what you are doing. E.g. 1,12 x 100. You can write 1,12 as 112 hundredths (as a common fraction) and when you multiply 112/100 by 100, the 100s will “cancel each other out”. The calculation can also be seen as 112 x 100/100 and thus, the answer will be 112. So, in other words, if you multiply with a multiple of 10, the comma in the answer will move the same number of spaces to the right as the number of zeros the multiple of 10 had.
If you have a calculation such as 0,4 x 0,12, also think about them as 4 tenths x 12 hundredths and follow the steps explained above. There is a shorter method that you can apply. Watch the video to see the shorter method. However, remember that you should always understand WHY you are applying steps in your quest to determine the answer.