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3rd-5th Grade Math: Practice & Review37 chapters | 252 lessons

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Instructor:
*T.J. Hoogsteen*

T.J. is currently a grade 5 teacher and Vice-Principal. He has a master's degree in Educational Administration and is working toward an Ed.D. in Educational Leadership.

In this lesson, you will learn a strategy called doubling to help multiply facts to ten. You will learn how to use known facts and double the product. Test your knowledge with a quiz at the end of the lesson!

Greek mythology tells the story of Heracles versus the Hydra, a water beast with several heads. During the battle, Heracles tried to defeat the monster by cutting off its heads. He learned very quickly that it wasn't such a good idea. Every time he cut off one head, two grew back. It's a long shot, but maybe this is also how Heracles learned to multiply by **doubling**.

As long as you know a few multiplication facts, you can use this strategy to figure out and learn new facts. To use this strategy, find a set of facts that is known to you. Then, double one factor (or add the number to itself), and double the **product**, or answer from the first set of facts.

For example, let's imagine there is a Hydra with 4 necks, each neck has 1 head, or 4 x 1=4. Now imagine that during a battle it loses all 4 heads, but each neck will sprout 2 new heads (doubling a factor, or 4 x 2), so to figure out how many heads it now has, we also have to double the original number of heads it had (or doubling the product). Remember, to double a number just add it to itself. So if 4 x 1 =4, then I double the second factor to make 4 x 2, I double the first answer (4 + 4), and I get 8 as my new product.

Now that I know 4 x 2, I can use doubling to help me figure out a new set of facts. I double the 2 (2 + 2) to get 4, now my new equation is 4 x 4. Well, if know that 4 x 2 is 8, and I doubled one factor, I then double the product (8 + 8) to get 16. So, I now know 4 x 4 is 16.

Doubling can also be used in reverse. For example, I may have trouble with knowing my multiplication facts related to 6. An important point is that this will only work if the fact I have trouble figuring out is an even number. But I know that 6 is 3 doubled and I'm good at my facts related to 3. So to help me figure out 5 x 6, I actually think about 5 x 3. I know 5 x 3 is 15. So if I have to double 3 to get 6 (my second factor), I also have to double the product. In this situation, if I double the product (15 + 15), I would get 30.

So, we have learned to use doubling as a strategy to learn new facts. Take a multiplication fact that you know, double one factor, and then double the product; this will give you your answer. This will be especially helpful if you encounter a mythological beast and accidentally remove its heads during battle. In that case, you will be able to figure our how many heads you will be now up against.

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3rd-5th Grade Math: Practice & Review37 chapters | 252 lessons

- Go to Addition

- Go to Subtraction

- How to Perform Multiplication: Steps & Examples 5:22
- How to Multiply One-Digit Numbers
- Using Mental Math for Multiplication 4:44
- Learning Multiplication Facts to 10 Using Commutative Property
- Learning Multiplication Facts to 10 Using Rectangular Array 4:02
- Learning Multiplication Facts to 10 Using Skip Counting
- Learning Multiplication Facts to 10 Using Doubling
- Multiplying a Two-Digit Number by a One-Digit Number
- How to Multiply Three or More Numbers
- How to Multiply Numbers Ending in Zeroes 2:56
- How to Complete the Multiplication Sentence
- Finding the Missing Factor 3:17
- Working with Multiplication Input-Output Tables
- The Relationship Between Multiplication & Division
- Go to Multiplication

- Go to Division

- Go to Angles

- Go to Money

- Go to Time

- Go to Integers

- Go to Percents

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