Lesson 9 Subtraction Algorithms (Part 2)

- Let’s learn more about our first subtraction algorithm.

Warm-up True or False: Does It Commute?

Decide if each statement is true or false. Be prepared to explain your reasoning.

$4 \times 5 = 5 \times 4$
$125 + 200 = 200 + 125$
$300 - 100 = 100 - 300$

Activity 1 Revise Subtraction Work

Lin’s work for finding the value of $428 - 156$ is shown.

Subtraction. Four-hundred plus twenty plus eight, minus one-hundred plus fifty plus six, equals three-hundred plus thirty plus two.

What error do you see in Lin’s work?
What would you tell or show Lin so she can revise her work?

Activity 2 Try the Algorithm

Here is a subtraction algorithm you saw in an earlier lesson:

Subtraction. Three-hundred plus ninety plus one, minus two-hundred plus ten plus five.

Try using this algorithm to find the value of each difference. Show your reasoning. Organize it so it can be followed by others.

$283 - 159$
$425 - 192$
$639 - 465$
$591 - 128$
$832 - 575$

Practice Problem

Problem 1

Write 518 and 346 in expanded form.
Use the expanded form to find the difference of the two numbers.