Section B: Practice Problems Decompose to Subtract

Section Summary

Details

In this section, we practiced subtracting two-digit numbers. We learned that when there are not enough ones to subtract by place, you can decompose 1 ten for 10 ones. We used base-ten blocks and base-ten diagrams to show our thinking.

Base ten diagram. 6 tens, and 3 ones. 2 tens crossed out and the 3 ones, crossed out. One of the crossed out tens has an arrow pointing to a circle with10 ones inside. 5 ones in the circle are crossed out. 

Problem 1 (Lesson 6)

Find the value of each difference. Show your thinking.

Problem 2 (Lesson 7)

Here is Mai’s work with a subtraction expression.

Base ten diagram. 8 tens and 5 ones. One of the tens is crossed out. An arrow points to a circle with 10 ones inside. The 5 ones are crossed and 2 ones inside the circle are crossed out.
  1. What subtraction expression does Mai’s diagram show?

  2. What is the value of the expression?

  3. Use Mai’s method to find the value of .

Problem 3 (Lesson 8)

Find the value of . Show your thinking. Use blocks if it helps.

Problem 4 (Lesson 9)

Here is how Clare found the value of .

Here is how Han found the value of .

Base ten diagram. 4 tens and 6 ones. 3 tens towers are crossed out. Arrow is pointing from one tower to a circle with 10 ones inside. The 6 ones are crossed out and 3 ones inside the circle are crossed out.

How are Han’s and Clare’s calculations the same?

How are they different?

Problem 5 (Lesson 10)

Find the value of each expression. Show your thinking.

Problem 6 (Exploration)

Here is Han’s method for finding the value of .




  1. Show each step of Han’s work with base-ten blocks.

  2. Explain or show why Han’s method works.

Problem 7 (Exploration)

Here is Jada’s method for finding the value of .

  1. Explain why Jada’s method works.

  2. Use Jada’s method to find the value of .