Addition & Subtraction Fluency Within 20 | Grade 2 Math

Addition and Subtraction Fluency Within 20 - Grade 2 Math
Grade 2 Math  ›  Addition & Subtraction Within 100  ›  Lesson 7
Grade 2 Math - Addition and Subtraction

Addition & Subtraction Fluency Within 20

Build confidence with addition and subtraction facts within 20. Learn to use make-ten facts, doubles, near doubles, and related addition and subtraction facts to solve accurately and efficiently.

Practice helpful mental strategies, recognize number relationships, find missing numbers, and explain how an answer can be checked. Understanding the strategies makes it easier to remember facts over time.

Addition within 20 Subtraction within 20 Make ten & doubles Related facts Grade 2 fluency

๐ŸŽฏ What You Will Learn

Recall and use addition facts
Add numbers with sums through 20 using a strategy that fits.
Recall and use subtraction facts
Subtract within 20 by counting back, making ten, or thinking of a related addition.
Use efficient mental strategies
Try make ten, doubles, near doubles, and counting on rather than counting every object.
Check your work and explain
Use fact families and the relationship between addition and subtraction to check answers.
For parents & teachers — standards alignment: CCSS 2.OA.B.2 focuses on fluently adding and subtracting within 20 using mental strategies; by the end of Grade 2, students should know from memory all sums of two one-digit numbers. Texas TEKS 2.4(A) likewise expects students to recall basic addition and subtraction facts within 20 with automaticity. This lesson revisits strategies from Grade 1 so students can develop accurate, flexible recall over time; its short story and unknown-number examples provide applications rather than replacing dedicated word-problem instruction.

๐Ÿง  Key Vocabulary

addend — a number being added.
sum — the total in an addition equation.
difference — the answer to a subtraction equation.
fluency — solving accurately and efficiently with strategies you understand and facts you remember.
make ten — break apart a number to complete a group of ten.
double / near double — an addition fact with equal addends / addends that differ by one.
related facts — addition and subtraction equations built from the same three numbers.
unknown number — a missing value shown with a blank, box, or symbol.

⚡ Fluent Does Not Just Mean Fast

A fluent math thinker finds correct answers, chooses a helpful mental strategy, and gradually remembers common facts without counting one by one. Speed grows with practice, but accuracy and understanding come first.

Remember the goal: for addition within 20, the sum is no more than 20; for subtraction within 20, you start with a number no greater than 20 and subtract an amount that does not make the answer negative.

๐Ÿงฉ Choose a Strategy That Fits

Count on9 + 3 = 12Start at 9 and say 10, 11, 12.
Make ten8 + 7 = 158 + 2 + 5 = 10 + 5.
Use doubles7 + 7 = 14A known double gives a quick sum.
Use near doubles7 + 8 = 157 + 7 = 14, then add 1.
Break apart to 1014 − 6 = 8First subtract 4, then subtract 2.
Think of addition15 − 9 = 6Ask: 9 + what makes 15?

๐Ÿ”Ÿ Make Ten with 8 + 7

Start with 8 and 7. Move 2 from the group of 7 to the group of 8. Now the first ten-frame is full and 5 are left over: 8 + 7 = 8 + 2 + 5 = 10 + 5 = 15.

8 + 7 becomes 10 + 5

Red counters show the original 8; blue counters show the 7 broken into 2 and 5.

๐Ÿ‘ฏ Doubles and Near Doubles

If you remember a double, you can solve a nearby fact. For example, 8 + 8 = 16. Since 9 is one more than 8, 8 + 9 = 17.

8 + 8=16 → add 1 → 8 + 9=17

➖ Subtract by Reaching Ten

For 14 − 6, take away 4 first to reach 10. There are still 2 more to take away: 14 − 4 = 10 and 10 − 2 = 8. So 14 − 6 = 8.

14−4 →10 −2 →8
Watch out: when you break 6 into 4 and 2, you must subtract both parts. Stopping at 10 would mean you subtracted only 4, not all 6.

๐Ÿ” Addition and Subtraction Belong Together

When the two addends are different, you can write four distinct related facts. For example, when you know that 6 + 9 = 15, you also know that 15 − 9 = 6.

6 + 9 = 15 9 + 6 = 15 15 − 6 = 9 15 − 9 = 6
Check subtraction with addition: for 17 − 8 = 9, check that 9 + 8 = 17. You can also find a missing addend by subtracting: 8 + □ = 15 means □ = 15 − 8 = 7.

๐ŸŽฏ A Short, Helpful Fluency Routine

Practice a few facts at a time. Use a strategy whenever an answer is not yet automatic. Once a fact feels familiar, try to recall it before checking.

1. LookRead the equation.
2. ThinkChoose a useful strategy.
3. SayGive the answer.
4. CheckUse a related fact.

๐ŸŒŸ 25 Worked Examples

Try each problem first. Then open “Show solution” to check the reasoning.
1Count on from the greater addend
Find 6 + 3.
Show solutionHide solution

Start at 6 and count on three: 7, 8, 9. So 6 + 3 = 9. Counting on from the larger addend avoids counting all the objects from 1.

2Change the order to make addition easier
Find 4 + 9.
Show solutionHide solution

Changing the order of addends does not change the sum. Think 9 + 4. Count on from 9: 10, 11, 12, 13. Therefore 4 + 9 = 13.

3Use a number pair that makes 10
Find 7 + 3.
Show solutionHide solution

Seven needs 3 more to make a full ten. Because 7 + 3 is a make-ten fact, 7 + 3 = 10.

4Make ten to solve 8 + 7
Find 8 + 7.
Show solutionHide solution

Break 7 into 2 + 5. Give 2 to 8 to make 10: 8 + 7 = 8 + 2 + 5 = 10 + 5 = 15.

5Make ten to solve 9 + 6
Find 9 + 6.
Show solutionHide solution

Nine needs 1 to make ten. Break 6 into 1 + 5: 9 + 6 = 10 + 5 = 15.

6Make ten from the larger addend
Find 6 + 8.
Show solutionHide solution

Think 8 + 6. Break 6 into 2 + 4: 8 + 2 = 10, and 10 + 4 = 14. So 6 + 8 = 14.

7Use a double fact
Find 7 + 7.
Show solutionHide solution

Seven plus seven is a known double. 7 + 7 = 14. Remembering doubles helps with nearby facts.

8Use a near double
Find 8 + 9.
Show solutionHide solution

Start from the double 8 + 8 = 16. Nine is one more than 8, so 8 + 9 is one more than 16: 17.

9Use another near double
Find 6 + 7.
Show solutionHide solution

The double 6 + 6 is 12. Replace one 6 with 7, which adds one more: 6 + 7 = 13.

10Add zero
Find 14 + 0.
Show solutionHide solution

Adding no objects does not change the total. Therefore 14 + 0 = 14.

11Take away to reach 10
Find 15 − 5.
Show solutionHide solution

Fifteen is 10 + 5. Taking away 5 leaves 10, so 15 − 5 = 10.

12Subtract by making a ten first
Find 13 − 4.
Show solutionHide solution

Take away 3 from 13 to reach 10. You still need to take away 1, so 13 − 4 = 10 − 1 = 9.

13Break apart the number being subtracted
Find 14 − 6.
Show solutionHide solution

Break 6 into 4 + 2. First 14 − 4 = 10, then 10 − 2 = 8. Therefore 14 − 6 = 8.

14Use addition to find a difference
Find 17 − 9.
Show solutionHide solution

Think: 9 plus what makes 17? From 9, add 1 to reach 10 and 7 more to reach 17. That is 1 + 7 = 8, so 17 − 9 = 8.

15Use a double to subtract
Find 16 − 8.
Show solutionHide solution

Because 8 + 8 = 16, subtracting one 8 from 16 leaves the other 8.

16Subtract from 20 using a related addition fact
Find 20 − 7.
Show solutionHide solution

Find the missing part in 7 + □ = 20. From 7, add 3 to reach 10, then add 10 more to reach 20. The missing part is 3 + 10 = 13. So 20 − 7 = 13. Check: 7 + 13 = 20.

17Subtract zero
Find 12 − 0.
Show solutionHide solution

Taking away nothing leaves the whole number. Therefore 12 − 0 = 12.

18Subtract a number from itself
Find 12 − 12.
Show solutionHide solution

Taking away all 12 from 12 leaves 0, so 12 − 12 = 0.

19Find an unknown addend
Find the missing number: 8 + □ = 15.
Show solutionHide solution

Think of the related subtraction: 15 − 8 = 7. Check: 8 + 7 = 15, so □ = 7.

20Find an unknown first addend
Find the missing number: □ + 6 = 14.
Show solutionHide solution

What goes with 6 to make 14? Since 14 − 6 = 8, the missing number is 8. Check: 8 + 6 = 14.

21Find a missing number in subtraction
Find the missing number: 17 − □ = 9.
Show solutionHide solution

Use the relationship between addition and subtraction: 9 + 8 = 17. Therefore 17 − 8 = 9.

22Check a true equation
True or false? 7 + 8 = 8 + 7.
Show solutionHide solution

Both sides equal 15. The order of addends does not change their sum. The statement is true.

23Write a complete fact family
Use 6, 9, and 15 to write two addition and two subtraction facts.
Show solutionHide solution

The four related facts are 6 + 9 = 15, 9 + 6 = 15, 15 − 6 = 9, and 15 − 9 = 6.

24Solve a short story with a known fact
Mia has 9 pencils. A friend gives her 7 more. How many does Mia have now?
Show solutionHide solution

Adding is appropriate because more pencils are joining the group. 9 + 7 = 9 + 1 + 6 = 10 + 6 = 16 pencils.

25Find and correct a subtraction mistake
A student writes 13 − 6 = 8. Is this correct? Explain.
Show solutionHide solution

No. Start at 13 and subtract 3 to make 10, then subtract 3 more to get 7. Check with addition: 7 + 6 = 13. The correct fact is 13 − 6 = 7.

๐ŸŽฎ Independent Practice — 30 Problems

Directions: solve each problem mentally when you can. For explanations, words, number sentences, or simple drawings are welcome. Check the answer key only after trying the problems.

  1. 7 + 5 = ___.
  2. 9 + 4 = ___.
  3. 6 + 6 = ___.
  4. 8 + 9 = ___.
  5. 5 + 7 = ___.
  6. 9 + 8 = ___.
  7. 0 + 13 = ___.
  8. 4 + 8 = ___.
  9. 7 + 9 = ___.
  10. 6 + 5 = ___.
  11. 15 − 7 = ___.
  12. 13 − 5 = ___.
  13. 18 − 9 = ___.
  14. 16 − 8 = ___.
  15. 20 − 6 = ___.
  16. 14 − 9 = ___.
  17. 11 − 4 = ___.
  18. 17 − 8 = ___.
  19. Find the missing number: 8 + ___ = 14.
  20. Find the missing number: ___ + 7 = 16.
  21. Find the missing number: 15 − ___ = 6.
  22. Find the missing number: 19 − ___ = 11.
  23. Use 8, 7, and 15 to write both addition facts.
  24. Use 9, 6, and 15 to write both subtraction facts.
  25. True or false? 8 + 6 = 7 + 7.
  26. Which sum is 16? A) 9 + 7   B) 8 + 5   C) 6 + 6.
  27. Avery has 12 stickers and gets 5 more. How many stickers are there now?
  28. A box holds 18 pencils. Nine are taken out for a class activity. How many pencils remain in the box?
  29. Show how to use make ten to find 9 + 7.
  30. A student says 14 − 8 = 7. Explain and correct the mistake.

๐Ÿ† Lesson Test — 15 Questions

Directions: work independently and check your answers when you finish. Accuracy and clear reasoning matter more than racing against a clock.

  1. 8 + 6 = ___.
  2. 9 + 7 = ___.
  3. 5 + 8 = ___.
  4. 7 + 7 = ___.
  5. 6 + 9 = ___.
  6. 12 − 5 = ___.
  7. 15 − 8 = ___.
  8. 19 − 9 = ___.
  9. 20 − 9 = ___.
  10. 16 − 7 = ___.
  11. Find the missing number: 7 + ___ = 15.
  12. Find the missing number: 17 − ___ = 9.
  13. True or false? 9 + 5 = 6 + 8.
  14. There are 8 red beads and 7 blue beads. How many beads are there in all?
  15. A student says 13 − 7 = 7. Explain why this is incorrect and give the correct answer.

๐Ÿ” Complete Answer Key

Show practice answer keyHide practice answer key

Practice Answers

Answer-key note: Equivalent equations and explanations are correct when the math and reasoning are correct. For fact-family items, either order of the two equations is fine.

1. 12
2. 13
3. 12
4. 17
5. 12
6. 17
7. 13
8. 12
9. 16
10. 11
11. 8
12. 8
13. 9
14. 8
15. 14
16. 5
17. 7
18. 9
19. 6
20. 9
21. 9
22. 8
23. 8 + 7 = 15 and 7 + 8 = 15.
24. 15 − 9 = 6 and 15 − 6 = 9.
25. True. Both sides equal 14.
26. A) 9 + 7 = 16.
27. 17 stickers; 12 + 5 = 17.
28. 9 pencils remain in the box; 18 − 9 = 9.
29. 9 + 1 + 6 = 10 + 6 = 16.
30. 14 − 8 = 6, because 8 + 6 = 14 (not 8 + 7).
Show test answer keyHide test answer key

Test Answers

Answer-key note: Accept an equivalent explanation or number sentence when it shows correct reasoning.

1. 14
2. 16
3. 13
4. 14
5. 15
6. 7
7. 7
8. 10
9. 11
10. 9
11. 8
12. 8
13. True. Both sides equal 14.
14. 15 beads; 8 + 7 = 15.
15. 13 − 7 = 6. The check is 7 + 6 = 13, but 7 + 7 = 14.

๐Ÿ’ก Common Mistakes to Watch For

Counting all instead of using known facts
Try to count on from the larger number or use make ten, doubles, or near doubles.
Breaking apart only part of a subtraction
In 14 − 6, subtracting 4 reaches 10, but you must subtract the other 2 as well.
Confusing a sum with a difference
8 + 6 = 14, while 14 − 6 = 8. Check with a related addition fact.
Guessing an unknown number
For 7 + □ = 15, use the related subtraction 15 − 7 = 8.
What comes next: Lesson 8 begins adding two-digit numbers within 100 using place value. Strong facts within 20 will help you add ones and tens more efficiently.

๐Ÿ”— Related Lessons

Grade 1 — Addition Strategies Within 20 Review counting on, make ten, and familiar addition facts. Grade 1 — Subtraction Strategies Within 20 Review counting back and using a ten to make subtraction easier. Grade 1 — Doubles, Near Doubles & Easier Facts Use familiar doubles to remember nearby sums. Grade 1 — Fact Families: Addition and Subtraction Practice the connection between related addition and subtraction facts.

๐Ÿ–จ️ Printable Companion

A future Addition & Subtraction Facts Within 20 Practice Pack can include short daily fact sets, make-ten puzzles, doubles and near doubles, related-fact cards, missing-number equations, mixed review, and a complete answer key.

← Lesson 6: 10 More, 10 Less, 100 More & 100 Less Grade 2 Math Hub Next: Add Within 100 Using Place Value →

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