Elementary School Math Quiz: Fluently Add And Subtract Within 20
20 questions · exam conditions
0:00
Fluently Add And Subtract Within 20Question 1 of 20

Solve: 16−916 - 9

7
9
8
6
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Elementary School Math Quiz

Elementary School Math Quiz: Fluently Add And Subtract Within 20

Practice Fluently Add And Subtract Within 20 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 Fluently Add And Subtract Within 20, 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

Solve: 16−916 - 9

  1. 7 (correct answer)
  2. 9
  3. 8
  4. 6
Explanation: Subtracting 9 from 16 gives 7. Choice B, 9, just repeats the number being subtracted instead of finding the difference. Choice C, 8, is off by one from a subtraction slip. Choice D, 6, is off by one further in the same direction.

Question 2

16−?=816 - ? = 8. What number goes in the blank?

  1. 8 (correct answer)
  2. 9
  3. 7
  4. 6
Explanation: 16 minus 8 equals 8, so 8 goes in the blank. 9 is close, but 16 minus 9 equals 7, not 8. 7 is close, but 16 minus 7 equals 9, not 8. 6 is too small; 16 minus 6 equals 10, not 8.

Question 3

What is 18−618 - 6?

  1. 1010
  2. 1111
  3. 1212 (correct answer)
  4. 1414
Explanation: Subtracting 6 from 18 gives 12, so C is correct. A is incorrect because it is too small to be the correct difference. B is incorrect because it is also too small, off by one from the correct answer. D is incorrect because it is too large to be the correct difference.

Question 4

Look at this pattern: 15−8=715 - 8 = 7, 14−7=714 - 7 = 7, 13−6=713 - 6 = 7. What subtraction problem comes next in this pattern?

  1. 14−7=714 - 7 = 7
  2. 12−5=712 - 5 = 7 (correct answer)
  3. 11−4=711 - 4 = 7
  4. 10−3=710 - 3 = 7
Explanation: The pattern decreases both numbers in each subtraction by 1 while keeping the difference at 7, so following 13−6=713-6=7 the next step is 12−5=712-5=7, matching B. A repeats an earlier step in the pattern instead of continuing it. C decreases the first number by 2 instead of 1, breaking the pattern. D decreases the first number by 3 instead of 1, breaking the pattern even further.

Question 5

Carlos has 66 red marbles and 77 blue marbles. He trades 44 red marbles for 44 green marbles. How many marbles does Carlos have in total now?

  1. 99 marbles total
  2. 1111 marbles total
  3. 1313 marbles total (correct answer)
  4. 1717 marbles total
Explanation: Carlos starts with 6 + 7 = 13 marbles total. When he trades 4 red marbles for 4 green marbles, he still has the same total number of marbles: 13. Choice A (9) incorrectly subtracts the traded marbles. Choice B (11) subtracts 2 from the original total. Choice D (17) incorrectly adds the 4 green marbles to the original total.

Question 6

Solve: 14−914 - 9

  1. 6
  2. 5 (correct answer)
  3. 9
  4. 4
Explanation: 14 minus 9 equals 5, so B is correct. A represents 6, an off-by-one error in the subtraction. C repeats the number 9 from the original problem instead of solving it. D represents 4, another off-by-one error in the opposite direction.

Question 7

Solve 13−813 - 8.

  1. 5 (correct answer)
  2. 6
  3. 4
  4. 8
Explanation: 13 minus 8 equals 5, which is the correct difference. Choosing 6 or 4 reflects a small counting or subtraction error near the correct answer. Choosing 8 mistakenly repeats the subtrahend instead of solving for the difference.

Question 8

Calculate 9+89 + 8.

  1. 18
  2. 17 (correct answer)
  3. 16
  4. 15
Explanation: Adding the two numbers, 9+8=179 + 8 = 17, so B is correct. Choice A is one more than the correct sum, which can happen from miscounting by one. Choice C comes from doubles confusion, treating the problem like 8+88 + 8 instead of 9+89 + 8. Choice D is two less than the correct sum, likely from a similar counting error.

Question 9

Maya has 9 stickers and gets 7 more. How many stickers now?

  1. 13
  2. 14
  3. 16 (correct answer)
  4. 15
Explanation: The correct answer is 16, because 9 + 7 = 16. Choice A (13) is too low for this sum. Choice B (14) is also too low, off by two. Choice D (15) is one sticker short of the correct total.

Question 10

Ben has 4 more stickers than Anna. Anna has 8 stickers. How many stickers does Ben have?

  1. 12 (correct answer)
  2. 4
  3. 8
  4. 16
Explanation: Anna has 8 stickers, and Ben has 4 more than that, so 8 plus 4 equals 12. 4 would be the difference if you subtracted instead of added. 8 is just Anna's amount, not Ben's. 16 would be too many for 4 more than 8.

Question 11

16−‾=816 - \underline{\hspace{2em}} = 8. What number goes in the blank?

  1. 9
  2. 16
  3. 8 (correct answer)
  4. 7
Explanation: This question tests 2nd grade fluency in adding and subtracting within 20, meaning solving these facts quickly and accurately using mental strategies or automatic recall (CCSS 2.OA.B.2: Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers). Fluency means answering quickly and correctly, ideally within a few seconds. Strategies for fluency include: (1) Make ten—decompose to make 10 first (8+7 → 8+2+5 → 10+5=15); (2) Doubles—know doubles facts (7+7=14), use for near doubles (7+8: one more than 7+7, so 15); (3) Think addition for subtraction (15-8: think '8 plus what equals 15? 8+7=15, so answer is 7'); (4) Fact families—if know 8+7=15, then know 15-7=8 and 15-8=7; (5) Memorization—automatic recall of facts. By end of 2nd grade, students should know these facts from memory. In this problem, find missing number in 16- =8. To solve fluently, use think addition (8 plus what equals 16? 8+8=16, so missing is 8), or fact families (know 8+8=16, so 16-8=8). Choice A is correct because for 16- =8: answer is 8 because 16-8=8 (verified by doubles: 8+8=16, so 16-8=8). This demonstrates fluency—quick, accurate calculation within 20. Choice B represents a common error like giving wrong value (gave 16 instead of 8, perhaps confusing with the total). This error typically happens when students misunderstand missing number problems or lack automatic recall. To help students achieve fluency: Practice facts daily—quick drills, flashcards, games, timed exercises (with emphasis on improvement, not pressure). Teach strategies explicitly: make ten (show with ten frames or fingers: 8 fingers up, need 2 more to fill 10, take 2 from 7 leaving 5, now 10+5=15), doubles (memorize 6+6, 7+7, 8+8, 9+9), near doubles (one more/less than double). Build fact families: if practice 8+8=16, also practice 16-8=8—reduces facts to learn. Use games: card games, online fact practice, partner quizzes. Connect strategies: 'You can solve 16-8 by thinking: what plus 8 equals 16? We know 8+8=16, so 16-8=8.' Spiral review: keep practicing previously learned facts while introducing new ones. Celebrate progress toward automatic recall: 'You answered in 2 seconds—that's fluency!' Identify which facts each student still needs to work on, target practice. Use manipulatives initially (counters, ten frames) but fade toward mental calculation. Watch for: slow counting strategies (need to build toward recall), basic fact errors (16-16≠8), confusion between addition and subtraction, not using efficient strategies, giving up without trying mental strategies.

Question 12

If 7+8=157 + 8 = 15, what is 15−715 - 7?

  1. 15
  2. 7
  3. 8 (correct answer)
  4. 6
Explanation: Subtracting, 15−7=815 - 7 = 8, so C is correct. Choice A repeats one of the numbers from the original fact instead of solving the new problem. Choice B repeats the other number being subtracted instead of the result. Choice D is two less than the correct difference, likely from a counting slip.

Question 13

What number added to 8 makes 15?

  1. 77 (correct answer)
  2. 66
  3. 88
  4. 1515
Explanation: Since 8 + 7 = 15, the missing number is 7, so Choice A is correct. Choice B is wrong because 8 + 6 = 14, not 15. Choice C is wrong because it repeats the number already given in the problem instead of finding the missing addend. Choice D is wrong because it repeats the total instead of finding the missing number.

Question 14

A store has 7 red pens and 8 blue pens. How many pens are there in all?

  1. 16
  2. 14
  3. 13
  4. 15 (correct answer)
Explanation: 7 red pens plus 8 blue pens is 15 pens total. A student might get 16 by rounding 7 up to 8 and doubling. A student might get 14 by only counting one type of pen twice. A student might get 13 by mixing up this fact with 8 + 5. Adding all the pens together, red and blue, gives 15.

Question 15

If 8+7=158+7=15, what is 15−715-7?

  1. 7
  2. 6
  3. 9
  4. 8 (correct answer)
Explanation: The correct answer is 8, because 15 - 7 = 8. Choice A (7) is the number being subtracted, not the answer. Choice B (6) is one less than the correct difference. Choice C (9) is one more than the correct difference.

Question 16

What is 14−914 - 9?

  1. 5 (correct answer)
  2. 6
  3. 9
  4. 4
Explanation: 14 minus 9 equals 5. 6 is 1 too high for the correct difference. 9 is one of the original numbers in the problem, not the answer. 4 is 1 too low for the correct difference.

Question 17

What is 7+87 + 8?

  1. 15 (correct answer)
  2. 16
  3. 13
  4. 14
Explanation: 7 plus 8 equals 15. 16 is 1 too high for the correct sum. 13 is 2 too low for the correct sum. 14 is 1 too low for the correct sum.

Question 18

What is 9+89 + 8?

  1. 17 (correct answer)
  2. 18
  3. 16
  4. 15
Explanation: Adding 9 and 8 gives 17. Choice B is 1 more than the correct sum. Choice C comes from doubles confusion, treating the problem like 8 plus 8. Choice D is 2 less than the correct sum.

Question 19

If 7+8=157 + 8 = 15, what is 15−715 - 7?

  1. 6
  2. 15
  3. 8 (correct answer)
  4. 7
Explanation: Since 15 minus 7 equals 8, that is the correct answer. Choice A, 6, is off by one from a subtraction slip. Choice B, 15, just repeats the total instead of subtracting. Choice D, 7, repeats the number being subtracted instead of computing the difference.

Question 20

Calculate 8+58+5.

  1. 13 (correct answer)
  2. 12
  3. 14
  4. 15
Explanation: Adding 8 and 5 gives 13. Choice B, 12, is off by one below the correct total. Choice C, 14, is off by one above the correct total. Choice D, 15, is off by two above the correct total.