# How to Multiply by 10

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• 0:15 Multiplication
• 0:35 Multiplying by 10
• 1:22 Rule for Multiplying by 10
• 3:10 Examples of Multiplying by 10
• 3:48 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

In this lesson, you will practice multiplying whole numbers and decimals by 10. You will learn the rules that make it very easy to solve all multiplication by 10 problems.

## Multiplication

Multiplication is repeated addition and it is a very important skill for you to learn. It is one of the basic operations of math that you will need to use over and over again. Multiplication tells you how many times to add something together. For example, 4 * 10 is telling you to add the 4 ten times. You can picture it as having ten groups of 4 pies each that you have to add up. While you can multiply any two numbers, in this lesson, we will look specifically at problems that call for multiplication by 10.

## Multiplying by 10

Let's see what happens when we multiply by 10. The 4 * 10 turns into 4 + 4 + 4 + 4 + 4 + 4 + 4 + 4 + 4 + 4, or the 4 added ten times. What does this equal? It equals 40. Look at that. We have our 4 with a 0 at the end.

What about 6 * 10? What does that equal? It adds up to 6 + 6 + 6 + 6 + 6 + 6 + 6 + 6 + 6 + 6 = 60. Look at that again! We have our 6 with a 0 at the end. It looks like when we multiply by 10, we end up with our number with an added 0 at the end.

## The Rule

We can create a rule from this. When multiplying whole numbers by 10, simply add a 0 to the end of the number, and you will have your answer. So, 5 * 10 is a 5 with a 0 at the end: 50. 3 * 10 is a 3 with a 0 at the end: 30. What about 10 * 10? The rule still applies. We add a 0 at the end of 10: 100.

We can check all these answers by adding up our groups. 5 * 10 is ten groups of 5: 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 = 50. 3 * 10 is ten groups of 3: 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 = 30. And 10 * 10 is 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 = 100.

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