Lesson 7

The purpose of this lesson is for students to subtract a two-digit number from a two-digit number when a ten is decomposed when subtracting by place.

In previous lessons, students learned that decomposing a ten is sometimes necessary when subtracting two numbers. Students used connecting cubes and base-ten blocks to represent their methods when subtracting a one-digit number from a two-digit number.

In the fist activity, students use methods that make sense to them to subtract and compare their methods with a partner. In the activity synthesis, students make connections across different methods and representations and consider which tools and representations work best for them. In the second activity, students use base-ten blocks to represent expressions and decompose a ten when subtracting by place.

Students should have access to connecting cubes and base-ten blocks throughout the lesson and the cool-down.

• Create a set of cards from the blackline master for each group of 4.

How are base-ten blocks and diagrams supporting students in showing what they understand about decomposing a ten when subtracting by place?