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.

$63 - 18$

Problem 1 (Lesson 5)

Find the value of each difference. Show your thinking.

$60 - 5$
$76 - 9$

Problem 2 (Lesson 6)

Here is Mai’s work with a subtraction expression.

What subtraction expression does Mai’s diagram show?
What is the value of the expression?
Use Mai’s method to find the value of $51 - 9$ .

Problem 3 (Lesson 7)

Find the value of $55 - 39$ . Show your thinking. Use blocks if it helps.

Problem 4 (Lesson 8)

Here is how Clare found the value of $46 - 29$ .

$\begin{array}{l} 46 - 20 = 26 \\ 26 - 6 = 20 \\ 20 - 3 = 17 \\ 46 - 29 = 17 \end{array}$

Here is how Han found the value of $46 - 29$ .

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

How are they different?

Problem 5 (Lesson 9)

Find the value of each expression. Show your thinking.

$35 + 57$
$81 - 43$

Problem 6 (Exploration)

Here is Han’s method for finding the value of $73 - 58$ .

$58 + 2 = 60$
$60 + 10 = 70$
$70 + 3 = 73$
$2 + 10 + 3 = 15$

Show each step of Han’s work with base-ten blocks.
Explain or show why Han’s method works.

Problem 7 (Exploration)

Here is Jada’s method for finding the value of $73 - 58$ .

$73 - 60 = 13$

$13 + 2 = 15$

Explain why Jada’s method works.
Use Jada’s method to find the value of $85 - 49$ .