Multiplying by a multiple of 10

General

The students learn to solve multiplication problems in which one number is a multiple of ten.

Standards

CCSS.Math.Content.3.NBT.A.3

Learning objective

Students will be able to multiply with a multiple of 10.

Introduction

Have the students play memory in pairs. First they write a multiplication problem on a card, and on another card they write the answer.

Instruction

First explain that a times table problem is a multiplication problem in which you determine how much of an amount of something you have. For example, in the 2 times table you have 2 more each time. Next, explain how a multiplication problem is set up with the multiplication symbol and that the first number shows how many times something you have and the second number shows how many there are each time. State that you can also multiply larger numbers together. Then discuss the problem 5 x 40. Using the pencils, show how you can calculate a multiplication problem with a multiple of ten. Explain that you solve it using a helping problem. The helping problem is the problem, for which a 0 is taken away from the multiple of ten. Then the helping problem can be solved. Now, to get to the answer of the original problem, you add the 0 back on. In the picture, there are 40 groups of 3 pencils. You can first solve the problem 4 x 3. Then the 0 is added back to the answer. Have the students write the problems down on their own and solve the problems with the balloons and the boxes. Ask how they solved these problems. Did they use the helping problem? Next you show a few problems for which the zero rule should be applied and have the students practice solving problems with one multiple of ten. Finally, you show how you can solve a story problem. You have the students determine what type of problem it is, which numbers you need to make the problem and how to solve it. Have the students solve the next couple story problems on their own.

Check whether the students can multiply with a multiple of 10 with the following questions:
- What is a helping problem?
- How do you solve 70 × 5?

Quiz

Students practice their understanding of multiplication with a multiple of ten in 10 exercises. Some of these have a visual aid, some are just number problems and some are in the form of a story problem.

Closing

You discuss once again with the students that it is important to be able to multiply with one multiple of 10, because that is how you can solve multiplication problems with large numbers by using a helping problem. As a closing activity you divide the class into four groups. Two groups come to the front of the class and stand in rows across from one another. The first student in the row competes with the first student in the other row. You state a multiplication problem and the student who gives the correct answer first can stay standing. The other student must sit down. The next student in the row then competes against the student that got the answer correct. The group that has the most students remaining in the end wins.

Teaching tips

Have students that have difficulty with multiplying with a multiple of 10 practice the 1 through 10 times tables. Have students use concrete materials such as blocks or have them write down the multiplication problems on a sheet of scrap paper.