Multiplying Decimals

Lesson Plan - Get It!

Audio:

Multiplying decimals is a lot like multiplying whole numbers.

All you need to do is pretend that the decimal is invisible. Then, you multiply the two factors together to find a product. After you find the product, decide where to put the decimal point.

To begin, take a look at an example. What is 18.5 x 2?

The product of 185 and 2 is 370. Now, where do you think the decimal point goes in the answer?

The product will have as many decimal places as the two numbers you multiplied together. You can count the decimal places by moving backwards from the end of each number, from right to left:

To see more examples of multiplying decimals, watch a Study Jams! video, Multiplication of Decimals (This video requires Adobe Flash Player. If you have trouble playing the video, have a parent or teacher help you download Flash Player).

1. Click the green STEP BY STEP button to begin.
2. Read or listen to the problem. Use the NEXT and SHOW ME! buttons to move on to the next steps.
3. As you watch the video, take notes on a separate sheet of paper.

What six steps can you use to multiply decimals? Share what you learned from the video with a parent or teacher.

Review the six steps:

1. Set up the problem vertically.
2. Multiply the first factor by the digit in the ones place of the second factor.
3. Multiply the first factor by the digit in the tens place of the second factor.
4. Add the two numbers.
5. Count the decimal places in both numbers being multiplied. The total number of decimal places will be the number of decimal places in the product.
6. Start counting decimal places in the product to the right of the last digit. Add the decimal point to the product to get your final answer!

Remember, if you are multiplying by a 1-digit number, like the example above, you can skip Steps 3 and 4!

• What steps are the same when multiplying decimal numbers and multiplying whole numbers?
• What steps are different?
• How do you think you can check your answer when you multiply decimal numbers?

Use the six steps for multiplying decimal numbers in the Got It? section, where you will learn how to check your answer and try some practice problems on your own.