Lesson 10 Subtraction Algorithms (Part 3)

    • Let’s learn another algorithm to subtract.

Warm-up Notice and Wonder: Digits that Disappear

What do you notice? What do you wonder?

Addition. Three-hundred plus twenty plus five.
Three-hundred twenty-five, with the three and the two crossed out in red, a two over the three in blue and a twelve over the two in blue.

Activity 1 A New Subtraction Algorithm

Andre and Clare found the value of . How they started their work is shown.

Andre’s algorithm

Subtraction. Five-hundred plus twenty plus eight, minus two-hundred plus seventy plus one.

Clare’s algorithm

Subtraction. Five-hundred twenty-eight minus two-hundred seventy-one.
  1. Complete both algorithms to find the difference.

  2. Andre and Clare started their subtraction in different ways. How did their way of starting affect the steps needed to find the difference?

Activity 2 Try Clare’s Algorithm

Clare used an algorithm to find the value of .

Try using her algorithm to find the value of each difference.

Subtraction. Five-hundred thirty-eight, minus one-hundred fifty-six, equals three-hundred eighty-two.

Practice Problem

Problem 1

  1. Use an algorithm of your choice to find the value of .

  2. Use an algorithm of your choice to find the value of .