Missing Numbers in Addition and Subtraction
Missing numbers in addition and subtraction means finding a number that is hidden in a sum. You see a blank or a box and you have to figure out what number goes there.
For example: 5 + ___ = 12. You need to find the number that, when added to 5, gives 12.
What is Missing Numbers in Addition and Subtraction - Class 2 Maths (Addition)?
A missing number problem is an equation with one number hidden. You use addition or subtraction to find it.
Three types of missing number problems:
- Missing addend: 7 + ___ = 15 (find what to add)
- Missing start number: ___ + 8 = 20 (find the starting number)
- Missing result in subtraction: ___ − 6 = 9 (find the number we subtract from)
Missing Numbers in Addition and Subtraction Formula
If a + b = c, then:
Missing b = c − a
Missing a = c − b
Solved Examples
Example 1: Missing Addend (Addition)
Question: 8 + ___ = 15
Think:
- What do we add to 8 to get 15?
- 15 − 8 = 7
Answer: 8 + 7 = 15
Example 2: Missing First Number (Addition)
Question: ___ + 9 = 17
Think:
- What number plus 9 gives 17?
- 17 − 9 = 8
Answer: 8 + 9 = 17
Example 3: Missing Number (Subtraction)
Question: 14 − ___ = 6
Think:
- What do we take away from 14 to get 6?
- 14 − 6 = 8
Answer: 14 − 8 = 6
Example 4: Missing Start Number (Subtraction)
Question: ___ − 5 = 13
Think:
- A number minus 5 gives 13
- Add back: 13 + 5 = 18
Answer: 18 − 5 = 13
Example 5: Word Problem — Tiffin Box
Question: Ria packed some ladoos in her tiffin. She ate 4 ladoos. Now she has 6 ladoos. How many did she pack?
Think:
- ___ − 4 = 6
- Add back: 6 + 4 = 10
Answer: Ria packed 10 ladoos.
Example 6: Word Problem — Collecting Stamps
Question: Arjun has 23 stamps. He gets some more stamps. Now he has 35 stamps. How many stamps did he get?
Think:
- 23 + ___ = 35
- 35 − 23 = 12
Answer: Arjun got 12 stamps.
Example 7: Two-Digit Missing Number
Question: 45 + ___ = 72
Think:
- 72 − 45 = 27
Answer: 45 + 27 = 72
Key Points to Remember
- To find a missing addend, subtract the known number from the total.
- To find a missing number being subtracted, subtract the answer from the bigger number.
- To find a missing start number in subtraction, add the answer and the number subtracted.
- Always check your answer by putting the number back into the equation.
- Addition and subtraction are opposite operations — they help each other.
Practice Problems
- Find the missing number: 6 + ___ = 14
- Find the missing number: ___ + 7 = 20
- Find the missing number: 18 − ___ = 9
- Dev has 34 marbles. He gives some to Kavi. Now Dev has 19 marbles. How many did he give?
- Find the missing number: ___ − 15 = 28
- Priya scored some runs. Then she scored 12 more. Her total is 30. How many did she score first?
Frequently Asked Questions
Q1. How do I find a missing number in addition?
Subtract the number you know from the total. For example, in 9 + ___ = 16, calculate 16 − 9 = 7. The missing number is 7.
Q2. How do I find a missing number in subtraction?
If the missing number is being subtracted (15 − ___ = 8), subtract the answer from the bigger number: 15 − 8 = 7. If the start number is missing (___ − 6 = 10), add: 10 + 6 = 16.
Q3. Why do we use subtraction to find missing addends?
Addition and subtraction are opposite operations. If adding gives the total, then subtracting from the total gives back the missing part.
Q4. How can I check my answer?
Put the missing number back into the equation and see if both sides are equal. For example, if 8 + ___ = 15 and you found 7, check: 8 + 7 = 15. Correct!
Q5. Can missing number problems have 2-digit numbers?
Yes. For example, 35 + ___ = 52. Solve it the same way: 52 − 35 = 17. The missing number is 17.
Q6. What if the missing number is the answer?
If the problem is 8 + 5 = ___, just add the two numbers: 8 + 5 = 13. The missing answer is 13.
