Elementary School Math Quiz: Determine Unknown Whole Numbers
20 questions · exam conditions
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Determine Unknown Whole NumbersQuestion 1 of 20

Sarah had 14 crayons. She lost some crayons and now has 6 crayons left. What number belongs in the box? 14−□=614 - \square = 6

20
9
8
7
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Elementary School Math Quiz

Elementary School Math Quiz: Determine Unknown Whole Numbers

Practice Determine Unknown Whole Numbers in Elementary School Math with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Determine Unknown Whole Numbers, giving you a quick way to practice the rules, question types, and explanations that matter most for Elementary School Math.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

Sarah had 14 crayons. She lost some crayons and now has 6 crayons left. What number belongs in the box? 14−□=614 - \square = 6

  1. 20
  2. 9
  3. 8 (correct answer)
  4. 7
Explanation: Sarah started with 14 crayons and has 6 left, so she lost 14 - 6 = 8 crayons. We can check: 14 - 8 = 6 ✓. Choice A (20) gives 14 - 20 = -6. Choice B (9) gives 14 - 9 = 5. Choice D (7) gives 14 - 7 = 7.

Question 2

Solve: 3+9= ?3 + 9 = \ ?

  1. 13
  2. 9
  3. 11
  4. 12 (correct answer)
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When finding the result in addition (like in 3 + 9 = ?), we add the numbers: 3 + 9 = 12. Use counting or known facts. The equation is 3 + 9 = ?. Choice D is correct because 3 + 9 = 12, so ? = 12. Choice A is a common error like adding wrong (3 + 10 = 13), due to calculation mistake. To help students: Teach direct addition; use counters; practice checking; connect to fact families; provide many examples.

Question 3

Which number makes this equation true? 12=?+512 = ? + 5

  1. 8
  2. 17
  3. 6
  4. 7 (correct answer)
Explanation: We need to find what number plus 5 equals 12. Since 7 + 5 = 12, the answer is 7. Choice A (8) gives 8 + 5 = 13. Choice B (17) gives 17 + 5 = 22. Choice C (6) gives 6 + 5 = 11.

Question 4

Maria has some stickers. She gives 4 stickers to her friend and has 7 stickers left. Which equation shows how many stickers Maria had at the start?

  1. ?+4=7? + 4 = 7
  2. ?−4=7? - 4 = 7 (correct answer)
  3. 4+7=?4 + 7 = ?
  4. 7−4=?7 - 4 = ?
Explanation: Maria started with some unknown number of stickers (?), gave away 4, and had 7 left. This gives us ? - 4 = 7. Choice A incorrectly adds instead of subtracts. Choice C finds the total after giving away, not the original amount. Choice D finds how many were given away, not the original amount.

Question 5

What number makes this equation true: 7+5=□7 + 5 = \square?​

  1. 11
  2. 12 (correct answer)
  3. 5
  4. 13
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When finding the result in an addition equation (like in a + b = ?), we simply compute the sum by adding the two addends together. We can use counting on or known facts to find the total efficiently. The equation is 7 + 5 = □. Choice B is correct because 7 + 5 = 12, so □ = 12. Choice A is a common error where students make a calculation mistake, such as adding 7 + 4 = 11 instead of 7 + 5, which happens because they may miscount or confuse the numbers. To help students: Teach each unknown position explicitly (result, addend, start); show how to check answer by substituting back into equation; for result unknown, it's direct computation; use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; emphasize checking: substitute answer back into equation to verify it's true; provide many examples with unknowns in all positions.

Question 6

Find the missing number: 9−4= ?9 - 4 = \ ?

  1. 13
  2. 4
  3. 6
  4. 5 (correct answer)
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When finding the result in a subtraction equation (like in a - b = ?), we compute the difference by subtracting the subtrahend from the minuend. We can think of it as counting back or using related addition facts to verify. The equation is 9 - 4 = ?. Choice D is correct because 9 - 4 = 5, so ? = 5. Choice A is a common error where students add instead of subtract, like 9 + 4 = 13, which happens because they may not recognize the operation or confuse addition and subtraction symbols. To help students: Teach each unknown position explicitly (result, addend, start); show how to check answer by substituting back into equation; for result unknown in subtraction, connect to addition (if 9 - 4 = 5, then 5 + 4 = 9); use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; show related fact families; emphasize checking: substitute answer back into equation to verify it's true; provide many examples with unknowns in all positions.

Question 7

Find the missing number: 9 - 4 =  .

  1. 4
  2. 5 (correct answer)
  3. 6
  4. 13
Explanation: When you see a subtraction problem like 9 - 4, you're being asked: "If I start with 9 things and take away 4, how many are left?" One great way to solve this is to count backward from the bigger number. Start at 9 and count back 4 steps: 9 → 8 → 7 → 6 → 5. After taking away 4, you land on 5. You can also check your work by adding: 5 + 4 = 9, which matches the number you started with. That confirms 5 is correct! Now let's look at why the other answers don't work. The choice 4 is the number you were subtracting, not the amount left over — it's easy to accidentally repeat a number from the problem. The choice 6 happens if you only count back 3 steps instead of 4, so you stopped one number too early. The choice 13 comes from adding 9 + 4 = 13 instead of subtracting — remember, the minus sign (-) means take away, so the answer should be smaller than 9, not bigger. A helpful strategy: whenever you subtract, the answer should be less than the number you started with. If your answer is bigger, you probably added by mistake. And you can always double-check subtraction by adding your answer back — if it returns you to the starting number, you got it right!

Question 8

Solve: 6+?=146 + ? = 14. What is ??

  1. 8 (correct answer)
  2. 20
  3. 6
  4. 7
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is an addend (like in a + ? = c), we need to find what number added to a equals c; we can think of this as subtraction: c - a = ?. Or we can count on from a to c and count how many—that's the unknown. The equation is 6 + ? = 14. Choice A is correct because when we add 6 + 8 = 14, so the unknown is 8. Choice B is a common error where students add the two given numbers instead of subtracting, getting 6 + 14 = 20; this happens because finding unknowns in different positions requires different strategies and the inverse relationship between operations must be understood. To help students: Teach each unknown position explicitly (result, addend, start); show how to check answer by substituting back into equation; for addend unknown, connect to subtraction and 'unknown addend' thinking (covered in CCSS.1.OA.4); use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; show related fact families (if 6+8=14, then 14-6=8); emphasize checking: substitute answer back into equation to verify it's true.

Question 9

Find the missing number: 4 +   = 9.

  1. 4
  2. 5 (correct answer)
  3. 6
  4. 13
Explanation: When you see a problem like 4 +   = 9, you're being asked to find the missing part of an addition sentence. The trick is to think: "I have 4, and I want to get to 9. How many more do I need to count up?" One great way to solve this is to count up from 4 until you reach 9: 5, 6, 7, 8, 9 — that's 5 numbers, so you need to add 5. You can check your work by putting it back into the sentence: 4 + 5 = 9. It works! Now let's look at why the other answers don't fit. Choosing 4 repeats the number already in the problem, but 4 + 4 = 8, which is too small. Choosing 6 overshoots, since 4 + 6 = 10, one too many. Choosing 13 is what you get if you accidentally add the two numbers you see (4 + 9 = 13) instead of finding the missing piece — but 13 is even bigger than 9, so it can't be right when you're building up to 9. A helpful tip: whenever a number is missing in an addition sentence, you can count up from the number you have to the total, or think about subtraction — the missing number is 9 - 4 = 5. Always plug your answer back in to make sure both sides equal the same amount!

Question 10

Use the number line to find the missing number: 3+?=83 + ? = 8

  1. 4
  2. 5 (correct answer)
  3. 6
  4. 11
Explanation: Starting at 3 on the number line, we need to count how many spaces to reach 8. Counting: 4, 5, 6, 7, 8 shows we move 5 spaces. So 3 + 5 = 8. Choice A (4) gives 3 + 4 = 7. Choice C (6) gives 3 + 6 = 9. Choice D (11) gives 3 + 11 = 14.

Question 11

What number goes in the blank:   + 3 = 10?

  1. 6
  2. 7 (correct answer)
  3. 8
  4. 13
Explanation: When you see a problem like   + 3 = 10, you're being asked to find a missing addend — a hidden number that, when added to 3, gives you 10. A great trick for these is to think of it as a subtraction problem: if something plus 3 equals 10, then 10 - 3 tells you the missing number. Let's check: 10 - 3 = 7. And to be sure, put it back in: 7 + 3 = 10. It works! So 7 is the number that fills the blank. Now look at why the others don't fit. 6 is a common near-miss — 6 + 3 = 9, which is one short of 10. 8 overshoots — 8 + 3 = 11, one too many. 13 is a trap for students who added 10 and 3 instead of finding the missing piece; 13 + 3 = 16, way too big. Notice that 13 comes from doing the opposite operation, so watch out for that. Here's your takeaway: whenever you see a blank before the plus sign with a total on the other side, subtract the number you already know from the total. "To find a missing part, take the whole and subtract the part you have." Always plug your answer back in to double-check — that quick step catches almost every mistake.

Question 12

Emma writes the equation 6+4=5+?6 + 4 = 5 + ?. What number makes both sides equal?

  1. 4
  2. 5 (correct answer)
  3. 6
  4. 10
Explanation: The left side equals 6 + 4 = 10. For the equation to be true, the right side must also equal 10. So 5 + ? = 10, which means ? = 5. Choice A (4) gives 5 + 4 = 9. Choice C (6) gives 5 + 6 = 11. Choice D (10) gives 5 + 10 = 15.

Question 13

Complete the equation: □−2=8\square - 2 = 8

  1. 10 (correct answer)
  2. 6
  3. 8
  4. 12
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the minuend in subtraction (like in ? - b = c), we work backwards by adding the subtrahend to the result: c + b = ?. We can check by subtracting: ? - b should equal c. The equation is □ - 2 = 8. Choice A is correct because adding 8 + 2 = 10, and we can verify: 10 - 2 = 8. Choice D is a common error where students multiply or use a different operation, like 8 x 2 - something leading to 12, which happens because working backwards is less intuitive. To help students: Teach each unknown position explicitly (result, addend, start); show how to check answer by substituting back into equation; for minuend unknown, explicitly teach 'work backwards' by adding subtrahend to result; use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; show related fact families (if 10 - 2 = 8, then 8 + 2 = 10); emphasize checking: substitute answer back into equation to verify it's true; provide many examples with unknowns in all positions.

Question 14

Solve: □−5=7\square - 5 = 7. What is □\square?

  1. 2
  2. 12 (correct answer)
  3. 7
  4. 13
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the minuend in subtraction (like in ? - b = c), we work backwards by adding the subtrahend to the result: c + b = ?. We can check by subtracting: ? - b should equal c. The equation is □ - 5 = 7. Choice B is correct because 7 + 5 = 12, and we can verify: 12 - 5 = 7. Choice A is a common error where students subtract instead of adding, getting 7 - 5 = 2; this happens because working backwards is less intuitive and they don't use the inverse operation. To help students: Teach each unknown position explicitly (result, subtrahend, minuend); show how to check answer by substituting back into equation; for minuend unknown, explicitly teach 'work backwards' by adding subtrahend to result; use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; show related fact families (if 12-5=7, then 7+5=12); emphasize checking: substitute answer back into equation to verify it's true.

Question 15

Tom counted 9 birds in a tree. Then some more birds flew to the tree. Now there are 15 birds total. Which equation can help find how many birds flew to the tree?

  1. 9+?=159 + ? = 15 (correct answer)
  2. 15−9=?15 - 9 = ?
  3. ?+15=9? + 15 = 9
  4. 9−?=159 - ? = 15
Explanation: Tom started with 9 birds, some unknown number (?) flew to the tree, and now there are 15 total. This gives us 9 + ? = 15. Choice B solves the problem but doesn't show the unknown. Choice C incorrectly suggests adding 15 to get 9. Choice D incorrectly uses subtraction when birds were added.

Question 16

Look at this equation: 8=3+?8 = 3 + ?. What number makes this equation true?

  1. 4
  2. 6
  3. 11
  4. 5 (correct answer)
Explanation: When you see an equation with a missing number, you're solving for what makes both sides equal. The equation 8=3+?8 = 3 + ? is asking: "What number do I add to 3 to get 8?" To find the missing number, think about it as a simple addition problem. You know that 3 plus some number equals 8. You can count up from 3 to 8: start at 3, then count 4, 5, 6, 7, 8. How many numbers did you count? You counted 5 numbers, so 3+5=83 + 5 = 8. You can also think of this as subtraction: 8−3=58 - 3 = 5. Let's check why each wrong answer doesn't work. Choice A (4) would give us 3+4=73 + 4 = 7, which is less than 8. Choice B (6) would give us 3+6=93 + 6 = 9, which is more than 8. Choice C (11) would give us 3+11=143 + 11 = 14, which is much bigger than 8. Only choice D (5) works: 3+5=83 + 5 = 8. Remember this helpful strategy: when you see a missing number problem like 8=3+?8 = 3 + ?, you can always check your answer by substituting it back into the equation. If 3+5=83 + 5 = 8, then you know 5 is correct. This checking method works for any missing number problem and helps you catch mistakes.

Question 17

Solve: 15−6= ?15 - 6 = \ ?

  1. 10
  2. 9 (correct answer)
  3. 6
  4. 8
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When finding the result in a subtraction equation (like in 15 - 6 = ?), we simply compute the operation by subtracting the second number from the first. We can think of it as taking away 6 from 15, counting backwards or using manipulatives. The equation is 15 - 6 = ?. Choice B is correct because 15 - 6 = 9, so ? = 9. Choice A is a common error where students might add instead of subtracting, getting 15 + 6 = 21, but subtraction requires understanding removal. To help students: Teach result unknown in subtraction as direct computation; use objects to model taking away; practice with number lines; emphasize checking by adding back (9 + 6 = 15); provide varied examples.

Question 18

Find the missing number: 18−□=1018 - \square = 10.

  1. 28
  2. 8 (correct answer)
  3. 10
  4. 7
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the subtrahend (like in 18 - ? = 10), we find what subtracted from 18 gives 10 by subtracting: 18 - 10 = 8. Or think as addition: 10 + 8 = 18. The equation is 18 - □ = 10. Choice B is correct because 18 - 8 = 10, so □ = 8. Choice A is a common error of adding, getting 18 + 10 = 28, not using inverse. To help students: Link to addition; use fact families; practice substitution; model with objects; teach unknown positions explicitly.

Question 19

Find the missing number: 9+□=149 + \square = 14.

  1. 5 (correct answer)
  2. 4
  3. 14
  4. 6
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is an addend (like in 9 + ? = 14), we need to find what number added to 9 equals 14, which can be done by subtracting: 14 - 9 = 5. We can also count on from 9 to 14 (10, 11, 12, 13, 14) and count the steps—that's 5. The equation is 9 + □ = 14. Choice A is correct because when we add 9 + 5 = 14, so the unknown is 5. Choice C is a common error where students might select the total instead of finding the missing part, not recognizing they need to use the inverse operation. To help students: Teach addend unknown by connecting to subtraction (CCSS.1.OA.4); use part-part-whole diagrams; practice checking by substituting; provide examples with objects; show fact families like if 9 + 5 = 14, then 14 - 9 = 5.

Question 20

What number makes this equation true: □+7=16\square + 7 = 16?

  1. 8
  2. 9 (correct answer)
  3. 23
  4. 7
Explanation: This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the starting number (like in ? + 7 = 16), subtract: 16−7=916 - 7 = 9. Check: 9+7=169 + 7 = 16. The equation is □+7=16\square + 7 = 16. Choice B is correct because 16−7=916 - 7 = 9, verifying 9+7=169 + 7 = 16. Choice C is a common error of adding (16+7=2316 + 7 = 23), not working backwards. To help students: Teach backward subtraction; use models; verify by substitution; show fact families; practice positions.