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.

Activity 1 Revise Subtraction Work

Lin’s work for finding the value of is shown.

Subtraction. Four-hundred plus twenty plus eight, minus one-hundred plus fifty plus six, equals three-hundred plus thirty plus two.
  1. What error do you see in Lin’s work?

  2. 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.

Practice Problem

Problem 1

  1. Write 518 and 346 in expanded form.

  2. Use the expanded form to find the difference of the two numbers.