Lesson 3 Count on or Count Back to Subtract

    • Let’s find the difference between numbers.

Warm-up Number Talk: Tens and Hundreds

Find the value of each expression mentally.

Activity 1 Jump Back, Back, Back

Jada and Andre found the value of .

Here is their work.

Jada’s Work

Base ten diagram. 3 hundreds, labeled 300. 7 tens, 2 crossed out, labeled 50. 5 ones, 4 crossed out, labeled 1.

Andre’s Work

Number line. No tick marks. Arrow from point at 375 to point at 355 labeled 20. Arrow from point at 355 to point at 351 labeled 4.

What do you notice? What do you wonder?

  1. Try Andre’s way to find the value of .

    Show your thinking. Use a number line if it helps.

    Blank number line.

  2. Find the value of in your own way.

    Show your thinking. Use a number line if it helps.

    Blank number line.

Activity 2 Who Spilled Paint?

Oh no! Diego spilled paint on his paper and now he can’t see all the numbers. Find the number hidden by the paint.

Equation with splatter. Splatter plus 540 equals 1000.

Find the number that makes each equation true.

  1. 250 + ink splash = 1,000
  2. 660 - 440 = ink splash
  3. 680 + ink splash = 900
  4. ink splash + 590 = 1,000
  5. 900 - 370 = ink splash

Practice Problem

Problem 1

Find the value of each difference. Show your thinking. Use a number line or base-ten blocks if it helps.