# How to multiply decimals by 10, 100 and 1000

*A quick guide to multiplying decimals by powers of ten*

The modern way of teaching this topic is to get you to move the entire number either one, two or three places to the left in a place value table. While I love place value tables and find them very useful, I feel that there is an easier way of looking at the whole multiplying decimals thing.

The method I use (which I was taught in school, several decades ago) is to **move the decimal point to the right**.

To multiply a decimal by **10**, you move the decimal point **one** place to the right.

For example:

123.42 x 10 = **1234.2**

and

22.9 x 10 = **229**

(This idea works even when you’re multiplying whole numbers rather than decimals. For example, you know that 48 x 10 = 480. You could think of the 48 as 48.0, and move the decimal point one place to get your answer of 480.)

To multiply a decimal by **100**, you move the decimal point **two** places to the right.

For example:

242.867 x 100 = **24,286.7**

Supposing you have a calculation like 8.7 x 100. You might think that there aren’t enough places to move the decimal point. However, you can simply add a couple of zeros after the 7, and then do the calculation:

8.700 x 100 = 870.0 = **870**

To multiply a decimal by **1000**, you move the decimal point **three** places to the right.

For example:

26.679 x 1000 = **26,679**

and

9.02 x 1000 = 9.0200 x 1000 = 9020.0 = **9020**

© Empress Felicity May 2012