# Multiplying by Multiples of 10

- Third Grade
- Math
- 55 minutes
- Standards: 3.NBT.A.3

10, 20, 30, and up! In this lesson, students learn strategies for multiplying one-digit numbers by multiples of ten (10 through 90) through practice problems and playing a fun, hands-on game.

### Learning Objectives

Student will be able to multiply a one-digit number by a multiple of ten.

## Lesson

### Introduction *(1 minutes)*

- Tell students that today, they will be learning how to multiply any one-digit number by a multiple of ten.
- Explain that your class will be focusing on two-digit multiples of ten for this lesson: 10, 20, 30, 40, 50, 60, 70, 80, and 90.

### Explicit Instruction/Teacher Modeling *(14 minutes)*

- On the board, write a list of sample multiplication problems, including the product. Each problem should have a one-digit number and a two-digit multiple of ten. For example:
*3 x 40 = 120, 5 x 60 = 300, 7 x 70 = 490, 2 x 50 = 100, 80 x 2 = 160, 40 x 4 = 160.* - Ask your students to turn to a neighbor and discuss any patterns they see.
- Request that your students share their thoughts after a few minutes of discussion. Students may report that they see the simple problem inside of the larger problem. For example:
*I see 7 x 7 in 7 x 70. The answer to 7 x 7 is 49, and the answer to 7 x 70 is 490. So there is an extra 0 on both sides of the equal sign.* - Tell the class they'll be learning different strategies for solving these types of problems.
- Write another sample problem on the board. For example:
*30 x 6* - Explain to your class that the first strategy they can use to solve this problem is the
**sketch strategy**. Draw straight lines to represent base-ten sticks, and include the correct number of "groups" (represented by the one-digit number in the problem) in your drawing. For example:*Draw a picture of 6 groups of 30.*`III III III III III III`

- To solve, model counting each base-ten stick (by tens) for an answer of 180.
- Keeping the same problem on the board, model a second strategy of
**underlining**by drawing a line under the one-digit number, and the number in the tens place of your two-digit number. In this example, you'll underline the numbers 3 and 6. This will reveal the basic math problem*3 x 6*. - Write your new basic equation on the board, including the product. In this case:
*3 x 6= 18*. - Explain to your class that the 18 represents the number of tens, or
*18 x 10 = 180*.

### Guided Practice/Interactive Modeling *(10 minutes)*

- Pass out a dry erase board and marker to each student.
- Instruct your students to write a multiplication problem on their dry erase board, such as
*7 x 30*. - Tell students that you would like them to solve this problem using the sketch strategy.
- Guide students to draw seven groups of 30 on their boards. It should look like this:
`III III III III III III III`

- Ask your students to count their base-ten sticks by tens to solve the equation. Your students should come up with 210 as the product.
- Instruct your students to solve the same problem using the second strategy. They must show their work on their individual dry erase boards.
- Tell your students to find the simple multiplication problem and write it on their board. For example:
*7 x 3*. Tell them to solve the simple multiplication problem. They should get a product of 21. - Choose a volunteer to tell you what 21 tens is, or 21 x 10. You should receive the answer 210.
- Monitor your class' understanding of these concepts. If students are doing well, move onto the next activity. If not, repeat these steps with one or two more problems.

### Independent Working Time *(15 minutes)*

- Instruct your class to find a partner for the next activity.
- Pass out Multiplying Madness Game Sheet and 10-sided die to each pair of students.
- Read the directions on the game sheet with the class, and answer any questions your students may have.
- Once you've answered any questions, instruct your students to begin playing.
- Circulate while your students are playing the game to answer any questions.

## Extend

### Differentiation

**Enrichment:**Challenge advanced students to write 3 word problems using multiples of ten on the back of their worksheets.**Support:**Work with a group of struggling students on the first three problems on the silly seahorses worksheet. Model and work step-by-step as a group to monitor understanding. Give students who are having trouble a multiplication table to work with.

## Review

### Assessment *(14 minutes)*

- Pass out a copy of the Silly Seahorses multiplication worksheet to each student.
- Students will work independently to complete the worksheet.
- As students complete the worksheet, check for understanding and reteach individuals as necessary.

### Review and Closing *(1 minutes)*

- Ask the students which strategy they liked using better today, making a sketch or solving the basic fact and the multiplying by ten. Encourage your class to talk with their partners about why they liked using that strategy best.
- Remind your students that either strategy will work for this type of problem when used correctly and as mathematicians, they can decide which strategy works best for them.

## Teacher Tips