How to Multiply by 4

Instructor: Dana Sparkman
How can you multiply by four, quickly and easily, often in your head? In this lesson, you will learn how to use the double twice strategy to multiply any number by four.

The Double-Twice Strategy

Have you ever heard the expression ''double trouble?'' How about ''double the fun'' or ''double dare?'' If you double something, that is like multiplying by two. For example, 3 x 2 is the same as 3 doubled (or 6). If you know how to double a number, you can easily multiply by four.

Multiplication Facts

Before you learn the doubling strategy, you can practice the 'fours' multiplication facts.

4 x 0 = 0

4 x 1 = 4

4 x 2 = 8

4 x 3 = 12

4 x 4 = 16

4 x 5 = 20

4 x 6 = 24

4 x 7 = 28

4 x 8 = 32

4 x 9 = 36

Since multiplication is repeated addition, you can also think of multiplying as ''fast addition.''

4 x 2 is the same as 4 + 4, or 8.

4 x 3 is the same as 4 + 4 + 4, or 12.

4 x 4 is the same as 4 + 4 + 4 + 4, or 16.

Now, let's learn about the doubling strategy.

Steps to Solving the Problem

Example 1:

Suppose you wanted to find out how many quarters are in $3.00. You know that there are four quarters in a dollar, so you need to multiply:

3 x 4 = ?

Step 1: Find the number that you are multiplying by 4. In this problem, that number is 3.

Step 2: Double that number once: 3 doubled is 6.

Step 3: Using the answer from the first doubling (in this case, 6), double that: 6 doubled is 12.

So, the answer to 3 x 4 is 12.

Example 2:

What if your teacher said that she needed 4 dozen colored pencils. How many colored pencils is that? You know that a dozen is 12, and that you need to multiply.

12 x 4 = ?

Step 1: Find the number that you are multiplying by 4. In this problem, that number is 12.

Step 2: Double that number once: 12 doubled is 24.

Step 3: Using the answer from the first doubling (in this case, 24), double that: 24 doubled is 48.

So, the answer to 12 x 4 is 48.

Check Your Work

There are a couple of ways that you can check your work. One way is by repeated addition and another way is by a traditional multiplication strategy.

Example 1:

3 x 4 = _

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