Checking Addition and Subtraction
Making mistakes in addition and subtraction is common. In Class 3, students learn methods to check their answers. The most important method uses the inverse relationship between addition and subtraction: addition undoes subtraction, and subtraction undoes addition.
Checking answers is a habit that prevents errors and builds confidence.
What is Checking Addition and Subtraction - Class 3 Maths (Addition and Subtraction)?
Addition and subtraction are inverse operations. This means:
If A + B = C, then C − B = A and C − A = B
If C − B = A, then A + B = C
Methods to check:
- Checking addition using subtraction: Subtract one addend from the sum. If you get the other addend, the addition is correct.
- Checking subtraction using addition: Add the difference to the smaller number. If you get the larger number, the subtraction is correct.
- Estimation: Round the numbers and check if the answer is reasonable.
Solved Examples
Example 1: Checking Addition Using Subtraction
Question: Check if 245 + 138 = 383 is correct.
Think:
- If correct, 383 − 138 should equal 245.
- 383 − 138 = 245 ✓
Answer: The addition is correct.
Example 2: Finding an Error in Addition
Question: Ria writes 356 + 127 = 473. Check her answer.
Think:
- Check: 473 − 127 = 346
- 346 is not equal to 356. The answer is wrong.
- Correct: 356 + 127 = 483
Answer: Ria's answer is incorrect. The correct sum is 483.
Example 3: Checking Subtraction Using Addition
Question: Check if 500 − 175 = 325 is correct.
Think:
- If correct, 325 + 175 should equal 500.
- 325 + 175 = 500 ✓
Answer: The subtraction is correct.
Example 4: Finding an Error in Subtraction
Question: Aman writes 612 − 258 = 364. Check his answer.
Think:
- Check: 364 + 258 = 622
- 622 is not equal to 612. Wrong!
- Correct: 612 − 258 = 354
Answer: Aman's answer is incorrect. The correct difference is 354.
Example 5: Checking by Estimation
Question: Priya adds 389 + 215 and gets 504. Use estimation to check.
Think:
- Round: 389 ≈ 400, 215 ≈ 200
- Estimate: 400 + 200 = 600
- 504 is too far from 600. Likely incorrect.
- Correct: 389 + 215 = 604
Answer: The estimate suggests an error. The correct answer is 604.
Example 6: Checking with Three Numbers
Question: Dev adds 120 + 85 + 45 = 250. Check the answer.
Think:
- 250 − 45 = 205
- 205 − 85 = 120 ✓
- All steps check out.
Answer: The addition is correct. 120 + 85 + 45 = 250.
Example 7: Word Problem with Check
Question: Meera had 350 stickers. She gave away 128 and says she has 222 left. Is she right?
Think:
- Check: 222 + 128 = 350 ✓
Answer: Yes, Meera is correct.
Example 8: Checking Subtraction by Re-adding
Question: Kavi calculates 754 − 389 = 365. Verify.
Think:
- 365 + 389 = 754 ✓
Answer: The subtraction is correct.
Example 9: Using Reverse Operation to Find a Missing Number
Question: ___ + 147 = 500. Find the missing number.
Think:
- Missing number = 500 − 147 = 353
- Check: 353 + 147 = 500 ✓
Answer: The missing number is 353.
Key Points to Remember
- Addition and subtraction are inverse operations.
- To check addition: subtract one number from the sum. If you get the other number, the addition is correct.
- To check subtraction: add the difference to the smaller number. If you get the larger number, the subtraction is correct.
- Estimation helps catch large errors quickly.
- Always check your work to avoid careless mistakes.
- The inverse relationship also helps find missing numbers.
Practice Problems
- Check if 234 + 178 = 412 is correct.
- Check if 500 − 236 = 274 is correct.
- Ria says 425 + 375 = 800. Is she right? Use subtraction to check.
- Aman says 700 − 345 = 365. Use addition to verify.
- Use estimation to check: 192 + 308 = 500.
- Find the missing number: ___ + 268 = 591.
- Find the missing number: 800 − ___ = 452.
Frequently Asked Questions
Q1. How do you check addition?
Subtract one of the numbers from the sum. If the result equals the other number, the addition is correct. For example, if 35 + 25 = 60, check: 60 minus 25 = 35.
Q2. How do you check subtraction?
Add the answer (difference) to the number that was subtracted. If you get the original number, the subtraction is correct. For example, if 80 minus 35 = 45, check: 45 + 35 = 80.
Q3. What are inverse operations?
Inverse operations undo each other. Addition and subtraction are inverse operations. If adding 5 gives 12, then subtracting 5 from 12 gives back 7.
Q4. How does estimation help check answers?
Round the numbers to the nearest ten or hundred and add or subtract. If your exact answer is very different from the estimate, recheck your work.
Q5. Can you use checking to find a missing number?
Yes. If you know the sum and one addend, subtract to find the other. If you know the minuend and difference, subtract to find the subtrahend.
Q6. Should you always check your answers?
Yes, especially for important calculations. Checking helps catch careless errors in carrying, borrowing, or writing digits.
Q7. What is the most common mistake in addition?
Forgetting to carry over when a column sum is 10 or more. Checking with subtraction catches this error.
Q8. Is checking addition and subtraction covered in NCERT Class 3?
Yes. Verifying addition and subtraction using inverse operations is part of the NCERT Class 3 Maths curriculum.
Related Topics
- Addition of 3-Digit Numbers
- Subtraction of 3-Digit Numbers
- Addition Without Regrouping (3-Digit)
- Addition With Regrouping (3-Digit)
- Addition Word Problems (Grade 3)
- Subtraction With Regrouping (3-Digit)
- Subtraction Without Regrouping (3-Digit)
- Subtraction Word Problems (Grade 3)
- Mental Math (Grade 3)
- Adding 4 or More Numbers
- Mixed Operations (Grade 3)
- Mixed Word Problems (Grade 3)
