1. Multiplying by Multiples of 10 and 100
Lesson 5.1
Multiplying by Multiples of 10 and 100

2. Set the Purpose
You have learned about the basic multiplication facts. Today, you will use those basic facts and patterns of zeros to multiply by multiples of 10 and 100.
Connect: What are some things that might come in groups of tens or hundreds? What might be an easy way to count things in groups of tens and hundreds?

3. Pose the Problem
3 x 4 =
3 x 40 =
3 x 400 =

4. Multiples What are some multiples of 10?

5. Practice Problems Find 3 x 50 =
First: Multiply by the digit in the tens place. Multiply: 3 x 5 = 15
Write one zero after x 50 = 150
So, 3 x 50 = 150

6. Practice Problems Find 3 x 500.
Multiply by the digit in the hundreds place.
Multiply: 3 x 5 = 15
Write two zeros after 15.
3 x 500 = 1,500
So, 3 x 500 = 1,500

7. Important!
When the product of a basic fact ends in zero, the answer will have an extra zero.
6 x 5 = 30
6 x 50 = 300
6 x 500 = 3,000

8. Practice problems on your own!
9 x 20 =
6 x 30 =
4 x 40 =
7 x 300 =
6 x 500 =

9. More Practice Problems!
8 x 30 =
4 x 200 =
7 x 100 =
20 x 9 =
600 x 4 =

10. Challenge Practice Problems
What happens if there are multiple zeros on both sides?
40 x 20 = ?
You add the number of zeros on both sides.
40 x 20 = 800
60 x 300 = ?

11. More practice problems!
8 x 3,000 =
50 x 4 =
60 x 200 =
7 x 90 =
800 x 5 =

12. Problem Solving
Last year, the 4th graders at school collected 500 cans of food for the food drive. This year’s 4th graders want to collect two times as many cans. How many cans do this year’s 4th graders hope to collect?

13. Problem Solving Challenge!
A 4th grader breathes about 50 gallons of air per hour. Ahmed, a 4th grader, arrives at school at 8 A.M. and leaves at 3 P.M. How many gallons of air does he breathe at school?

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