Lesson 9 Subtraction Algorithms (Part 1)

    • Let’s learn a new way to subtract.

Warm-up Number Talk: Subtraction Strategies

Find the value of each expression mentally.

Activity 1 From Drawings to an Algorithm

Jada and Kiran found the value of . Their work is shown.

Jada’s drawing

Student representation of a base ten diagram with 3 hundreds, 2 crossed out, 9 tens with 2 crossed out with arrow pointing to 1 ten with 4 crossed out and a one, crossed out.

Kiran’s algorithm

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

  1. Explain how Kiran’s algorithm starts.

  2. Explain how Kiran recorded the decomposition of the ten into more ones.

  3. Finish Kiran’s work.

Activity 2 Card Sort: Diagrams and Algorithms

Your teacher will give you a set of cards. Match each diagram with an algorithm.

Explain or show your thinking.

Practice Problem

Problem 1

Here is a subtraction calculation.

Subtraction. Five-hundred plus forty plus five, minus three-hundred plus sixty plus three, equals one-hundred plus eighty plus two.

  1. Explain what the 400 above the 500 means.

  2. Explain what the 140 above the 40 means.

  3. Explain how the calculation works to find .