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Parent guide · Grade 2 Math · Unit 5

Lesson 5.3 Subtracting Across Zeros

Written for the parent. Read the Say this lines aloud as they are, or in your own words. Answers for you are marked Listen for.

At a glance

Time
5 sessions of 20–25 minutes
Goal
Subtract when the top number has zeros.
You need
  • Pencil and crayons
Print
Worksheet A · Worksheet B · the lesson page

Steps

  1. Do this: Ask these out loud. Your child answers out loud; no paper needed.

    • Ask: “What number is ten less than 643?” Listen for: 633
    • Ask: “What number is ten less than 302?” Listen for: 292
    • Ask: “What number is ten less than 395?” Listen for: 385
    • Ask: “What number is ten less than 517?” Listen for: 507
    • Ask: “What number is ten less than 879?” Listen for: 869

  2. Say this: “400 − 168: there are no tens to trade, so trade a hundred for 10 tens, then a ten for 10 ones. 400 becomes 3 hundreds, 9 tens, 10 ones.”

    Say this: “Check by adding.”

    Say this: “Across zeros: regrouping through a 0 in the tens.”

  3. Show: 404 − 398 = ___

    Say this: “Ones: 4 is less than 8, and the next place holds 0, so regroup from the hundreds: 4 becomes 3 and each 0 in between becomes 9.”

    Say this: “14 − 8 = 6”

    Say this: “Tens: 9 − 9 = 0”

    Say this: “Hundreds: 3 − 3 = 0”

    Say this: “Check: 6 + 398 = 404”

    Answer: 6

    Show: Gideon had 830 men. He sent 647 home. How many men stayed?

    bar model

    Say this: “Unknown: how many are left.”

    Say this: “Bar model: the whole is 830; one part is 647; the other part is unknown.”

    Say this: “Equation: 830 − 647 = ?”

    Say this: “830 − 647 = 183”

    Say this: “Answer: 183 men stayed.”

    Answer: 183 men. 183 men stayed.

  4. Do this: Your child does these with you. Let them try first; help only after a real try.

    Ask: 700 − 55 = ___

    Listen for: 645

    If stuck: Ones: 0 is less than 5, and the next place holds 0, so regroup from the hundreds: 7 becomes 6 and each 0 in between becomes 9.

    Ask: 408 − 95 = ___

    Listen for: 313

    If stuck: Ones: 8 − 5 = 3

    Ask: 600 − 81 = ___

    Listen for: 519

    If stuck: Ones: 0 is less than 1, and the next place holds 0, so regroup from the hundreds: 6 becomes 5 and each 0 in between becomes 9.

    7 more practice items on the lesson page, and on Worksheet A and Worksheet B.

    • Writing 0 − 8 = 8.

  6. Price a few household items between 100 and 500 cents. Your child adds two prices on paper and checks with a partner. Then find how much more one costs than the other.

  7. Say this: “Tell me what you learned today. Show me with your hands or the counters if you like.”

    Listen for: Subtract when the top number has zeros.

  8. Count by tens and hundreds from any number, forward and back.

Spread over the week

5 sessions of 20–25 minutes. Stop while it is still going well.

  1. Session 1. Warm-up, then teach the new idea (steps 1 and 2).
  2. Session 2. Warm-up again, then show how with the examples.
  3. Session 3. Practice together, then play the game.
  4. Session 4. More practice on the worksheet, and the daily habit.
  5. Session 5. Quick check: narration and a few practice items. Move on when it is mostly right.