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Chapter 2: Addition with Regrouping

Adding 4-digit numbers when boxes overflow

CBSE: Addition with/without regrouping • ICSE: Place value exchange • Cambridge: Stage 3
👨‍👩‍👧 Parent/Teacher notes at bottom

📋 What You'll Learn

  1. Part 1: Adding when no box goes past 9
  2. Part 2: Adding when one box overflows
  3. Part 3: Chain reactions (many overflows)
  4. Practice: Predicting overflow
  5. Quiz: Thinking questions

💡 The Big Idea

Step 1 of 6
🐢 No speed pressure • 🧠 Understand, don't memorize • 💬 Explain what happens
✅

Part 1: No Regrouping

1
2,341 + 1,234
Ones: 1+4=5 ✓ Tens: 4+3=7 ✓ Hundreds: 3+2=5 ✓ Thousands: 2+1=3 ✓
All ≤ 9. No regrouping needed. Answer: 3,575
City A
2,341
+
City B
1,234
Overflow Forecast:
Th
H
T
O
Safe
Thousands
3
2+1
Hundreds
5
3+2
Tens
7
4+3
Ones
5
1+4
Total People
3,575
✨
When no box has more than 9, everything fits. No regrouping needed!
🌊

Part 2: With Regrouping

2
2,347 + 1,235
Ones: 7+5=12. More than 9! → Write 2, move 1 ten up.
Tens: 4+3+1=8 ✓ Hundreds: 3+2=5 ✓ Thousands: 2+1=3 ✓
Answer: 3,582
ONES
12!
→
TENS
+1
ONES
2
City A
2,347
+
City B
1,235
Total (after regrouping)
3,582
🌊
10 of anything = 1 of the next bigger thing. 10 ones = 1 ten. 10 tens = 1 hundred. That's all!
🌊🌊

Part 3: Chain Reaction! — When overflow causes more overflow

3
🎯 Many Boxes Overflow!
Let's try: 1,876 + 2,567

Ones: 6 + 7 = 13 → More than 9! Move 1 ten up.
Tens: 7 + 6 + 1 = 14 → More than 9! Move 1 hundred up.
Hundreds: 8 + 5 + 1 = 14 → More than 9! Move 1 thousand up.

One box leads to another. Stay calm. Go one box at a time.
Overflow Forecast:
Th
H
T
O
Multiple overflows!
Th
3
1+2
H
8+5
= ?
T
7+6
= ?
O
6+7
= ?
🔗
Many boxes may overflow. Don't worry. Same rule every time: 10 becomes 1.
🔮

Practice: Regrouping Predictor — Think before you add

4
0
Correct
0
Streak
3,456 + 2,789
Will the ONES box get more than 9?
✅ Yes, overflow
❌ No, fits
🏙️

Practice: Add Numbers — Combine two towns

5
0
Correct
Town A
2,456
+
Town B
1,789
🔧

Regrouping Rescue — Find the mistake

6
0
Fixed
2,456 + 1,789 = ?
One of these answers is WRONG. Which one?
4,135
Answer A
4,245
Answer B
🧘

Calm Calculator — Who solved it better?

7
3,456 + 2,789
Who got it right?
🏃
Speedy Sam
"Done in 10 seconds!"
6,135
🐢
Careful Cara
"Let me check each box..."
6,245
📝

Thinking Quiz — Check your understanding

8
0
Score
0
Total
Loading question...
👨‍👩‍👧 For Parents & Teachers
▼

🎯 What This Chapter Teaches

Regrouping (often called "carrying") happens because a place value box gets more than 9. We avoid the word "carry" because it hides the why. Instead, we explain: when you have 10 or more of something, 10 of them group together to make 1 of the next bigger thing.

💬 What to Say

  • "What do you notice about the ones box?"
  • "Can you predict which boxes will overflow?"
  • "Why did that 10 move up?"
  • "How would you explain this to a friend?"

🚫 What NOT to Say

  • "Just carry the 1" — This hides the WHY
  • "Do it faster" — Speed creates errors and anxiety
  • "That's wrong, try again" — Instead, explore why

✅ Signs of Understanding

  • Predicts overflows BEFORE calculating
  • Explains WHY regrouping happens, not just HOW
  • Stays calm during chain reactions
  • Can find and fix errors in others' work