Balance subtraction equations – up to three digits
key notes :
🧮 What is a Balanced Equation?
A balanced equation means both sides are equal.
👉 Left side = Right side
Example:
45 − 20 = 25 ✅
⚖️ Both Sides Must Stay Equal
If you change one side, you must change the other side in the same way to keep it balanced.
Example:
90 − 40 = 50
Add 10 to both sides:
(90 − 40) + 10 = 50 + 10 → 60 = 60 ✅
🔢 Three-Digit Numbers (100–999)
You will subtract using numbers with 3 digits.
Example:
345 − 120 = 225 ✅
🧠 Think of a See-Saw!
Balancing equations is like a see-saw ⚖️ — both sides should weigh the same.
If one side goes up ⬆️ or down ⬇️, fix the other side!
➖ Check by Subtracting Again
To see if an equation is balanced:
✅ Solve both sides
✅ Compare answers
If equal → Balanced
If not → NOT balanced ❌
🟩 Spot the Missing Number
Sometimes a number is missing.
Find the number that keeps both sides equal.
Example:
300 − ___ = 120
300 − 180 = 120
So the missing number is 180 ✨
🧩 Rewrite Both Sides
Always subtract first, then compare.
Example:
250 − 75 and 300 − 125
250 − 75 = 175
300 − 125 = 175
✅ Balanced!
📝 Use Number Line or Place Value
If subtraction is difficult, use:
🔹 Place value chart
🔹 Number line
🔹 Borrowing (regrouping)
🌟 Summary
| ✅ Balanced Equation | ❌ Not Balanced |
|---|---|
| 400 − 150 = 250 | 510 − 200 = 400 (310 ≠ 400) |
| 235 − 35 = 200 | 600 − 100 = 450 (500 ≠ 450) |
Learn with an example
Which number makes the equation true?
915 − 82 = 840 − ?
First, subtract 915 − 82:
915 − 82 = 840 − ?
833 = 840 − ?
Find the number that makes the subtraction number sentence true.
840 − ? = 833
Subtract 833 from both sides:
840 − ? − 833 = 833 − 833
7 − ? = 0
Now, find the number that goes in the blank space. Remember, when a number is subtracted from itself, the difference is zero. The number in the blank space must be 7.
The missing number is 7.
Which number makes the equation true?
407 − 84 = ? − 94
First, subtract 407 − 84:
407 − 84 = ? − 94
323 = ? − 94
Find the number that makes the subtraction number sentence true.
? − 94 = 323
Add 94 to both sides:
? − 94 + 94 = 323 + 94
? = 417
The missing number is 417.
Which number makes the equation true?
928 − ? = 941 − 120
First, subtract 941 − 120:
928 − ? = 941 − 120
928 − ? = 821
Subtract 821 from both sides:
928 − ? − 821 = 821 − 821
107 − ? = 0
Now, find the number that goes in the blank space. Remember, when a number is subtracted from itself, the difference is zero. The number in the blank space must be 107.
The missing number is 107.
Let’s practice!
