The Correct Way to Teach Multiplying by 10

How do you teach multiplying with 10? 

As you may have guessed, when multiplying by 10, the best way to teach is to "just add a zero". So, if I do 7 x 10, I will get  70. Similarly, 23 x 10, gives 230

BUT,  does this trick also work when you multiply a decimal number with 10? 

Let's give it a try, try multiplying 5.4 by 10. You will get 5.40, which is not the correct answer! 

So, why not learn the right way to multiply by 10. 

Let's try this. Instead of adding a zero, we will move each digit one place value to the left, then put a 0 in the spot with no value as a placeholder.

1 would become 10, 5 would become 50, 73 would become 730, 4.5 would become 43, etc. 

Now let's try to multiply with this new strategy:

7 x 10 would get us 70, which is correct.

23 x 10 would get us 230, which is correct.

 And 5.4 x 10 would get us 54, which is correct!

So, if you were taught to "just add a zero" when you multiply by 10, then try to unlearn that strategy and learn this one, because though it helps when you multiply a whole number with 10, it won't come in so handy when you try a decimal.

Credit: My 5th grade teacher for teaching me the correct way to multiply by 10.