Missing Number Questions with Answers (Simple Practice for Kids)
A missing number question, something like 5 + __ = 9, is one of the first times a child meets the idea behind algebra, long before anyone mentions the letter x. It's just a sum with one part hidden, and the job is to work out what that hidden part must be.
Children who get comfortable with these early usually find algebra far less intimidating a few years later, because the underlying idea — finding an unknown value — already feels familiar.
The simple trick: use the opposite operation
To find a missing number in addition, subtract the known number from the total. For 5 + __ = 9, subtract 5 from 9: 9 − 5 = 4. So the missing number is 4, and 5 + 4 = 9 checks out.
The same idea works in reverse for subtraction. For __ − 3 = 7, add 3 to 7: 7 + 3 = 10. The missing number is 10, and 10 − 3 = 7 checks out.
Missing numbers in multiplication and division
For 6 × __ = 24, divide 24 by 6: 24 ÷ 6 = 4. The missing number is 4, and 6 × 4 = 24 checks out.
For __ ÷ 5 = 3, multiply 3 by 5: 3 × 5 = 15. The missing number is 15, and 15 ÷ 5 = 3 checks out.
Missing numbers in number patterns
Missing numbers also show up in sequences, like 4, __, 12, 16, where the pattern jumps by 4 each time. Since 4 + 4 = 8, the missing number is 8.
Practice questions
- 5 + __ = 9. Answer: 4
- 12 − __ = 5. Answer: 7
- __ + 8 = 15. Answer: 7
- 6 × __ = 24. Answer: 4
- __ ÷ 5 = 3. Answer: 15
- __ − 3 = 7. Answer: 10
- 4, __, 12, 16 — find the missing number. Answer: 8
- 9 × __ = 45. Answer: 5
Common mistakes I see in the classroom
The most common slip is using the same operation as the question instead of the opposite one — trying to add for a missing number in an addition question, rather than subtracting to find it. Reminding a child that finding a missing piece needs the undoing operation, not the original one, usually fixes this quickly.
Another common mistake is not checking the answer by putting it back into the original question. A quick check — does 5 + 4 really equal 9? — catches nearly every error before it's written down as final.
Tips for parents
Turn everyday counting into a missing number game. "We have 3 apples and need 8 for the recipe — how many more do we need?" is exactly the same puzzle as 3 + __ = 8, just wrapped in a real situation.
Tips for teachers
I like using a blank box or a question mark in place of the missing number rather than a letter, especially with younger students. It keeps the question feeling like a puzzle rather than formal algebra, which comes naturally a little later.
How step-by-step learning tools help
A step-by-step maths tool can show exactly which opposite operation was used to find a missing number, work through unlimited fresh missing number questions, and let a child check their own answer by putting it straight back into the original sum.
Frequently asked questions
Why are missing number questions important? They build the same thinking skill needed for algebra later — working backwards from what you know to find what you don't, using the opposite operation.
At what age do children usually start missing number questions? Simple addition and subtraction missing number questions usually start around age 6 to 7, with multiplication and division versions following around age 8 to 9.
Is a missing number question the same as algebra? It's the same idea in a simpler form — a missing number question uses a blank or a symbol, while algebra uses a letter like x, but both are asking you to find an unknown value.
What if there's more than one missing number in a question? These are usually solved one step at a time, finding whichever missing number can be worked out first from the information given, then using that to find the next one.
How can I check a missing number answer is correct? Put the answer back into the original question in place of the blank, and check that both sides now match — if they do, the answer is correct.
Every Blank Space Has an Answer Hiding Behind It
A missing number question can look intimidating simply because part of it is hidden. Once a child trusts that the opposite operation always reveals what's missing, that blank space stops feeling like a trick and starts feeling like just another sum.