How to Multiply Decimals | Math Review
Hello, and welcome to the Mometrix video on multiplying decimals. Multiplying decimals may seem like a daunting challenge, but in this video, we’ll show you the techniques you need to decimate this decimal dilemma.
In order to understand decimals, you first have to understand place value.
Every number has a value based on its place relative to the other numbers. Let’s look at the number 1,762 (one-thousand, seven hundred, sixty-two). Based on place value, the number to the far left has the largest value.
In this case, the first number is in the “thousand” place. One times 1,000 equals 1,000.
The second number, which is in ‘hundreds place,” equates to 700. You get that because 7 multiplied by 100 equals 700.
The third number, six, is in the “10” place. Six times 10 equals 60.
Lastly, the 2 is in the’ one’ place, so 2 times 1 equals 2.
So you have:
Thousands place: 1 x 1,000 = 1,000
Hundreds place: 7 x 100 = 700
Tens place: 6 x 10 = 66
Ones place. 2 x 1 = 2
Now, any number behind the last number, in this case, the two (2) takes the “tenth” place. This is where decimals come into play. Let’s look at 1,762.8. The .8 (point eight) behind the number two (2) equals eight-tenths of one whole.
Now that you understand numbers and their place value, let’s take a look at how to multiply decimals.
You multiply decimals just like you would normal whole numbers. The trick is understanding how and when to move the decimal point, so you get the right answer.
We’ll use this equation to show how it’s done:
45.18 x 0.5
Remember place value. That means 45 and 18 hundredths multiplied by 0.5, or five-tenths. So let’s figure this out:
In solving the problem, pretend (for just a moment) that the decimal point isn’t there. That would give you this equation:
4518 x 5
You don’t need the zero since it doesn’t add anything to the equation. If we solve this equation, we get:
4518 x 5 = 22590
But you’re not done. We have to figure out where to place the decimal. Here’s how you do that.
Go back to the original equation and count how many numbers are behind each decimal point. In this case, there are three.
45.18 x 0.5
You’re almost done. Now that we know there are three numbers behind the decimals, we go back to our answer and place the decimal three places from the last number. Our first answer was 22,590.
This shows the decimal goes after the 22. Therefore, the answer is:
So that’s our look at multiplying decimals. As you can see, the concept seems much harder than it actually is. If you understand place value and how to move the decimal in the right place, you’ll do just fine.
I hope this video helped!
See you guys next time!