3-12 Subtracting a Group

3-12 Subtracting a Group

Math Message

• Make an array on your whiteboard for the following question: There are 5 rows of 4 chairs for a class show. Write a number model for the total number of chairs.

• Change your sketch to fit this situation: 4 people are not coming, so you need 4 fewer chairs. Write a number model that shows the new total number of chairs.

Solve

Danielle has 10 toy tricycles that each have 3 wheels. How many wheels are there all together?

Danielle lost 1 tricycle.

How many total wheels are there now?

Solve #1 on Math Journal Page 93

Multiple Choice

What helper fact does your first sketch show on #1?

• $4\times9=36$

• $4\times10=40$

Solve #2 on Math Journal Page 94

Open Ended

If you wanted to solve

 $4\times8$   using the subtracting-a-group strategy