Multiplying by Multiples of 10
Student will be able to multiply a one-digit number by a multiple of ten.
- 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.
- 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.
- 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 minute)
- 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.