Subtraction Strategies Within 20 | 1st Grade Math

Subtraction Strategies Within 20 - Grade 1 Math
Grade 1 Math  ›  Addition & Subtraction  ›  Lesson 10
Grade 1 Math - Addition and Subtraction

Subtraction Strategies Within 20

Learn useful subtraction strategies within 20 by counting back, subtracting to 10, counting on to find a difference, and using related addition facts.

This first grade subtraction lesson uses number paths, make-10 thinking, counting on, and visual models to help students choose efficient strategies and solve subtraction problems within 20 with understanding.

Subtraction within 20 Count back Subtract to 10 Count on Grade 1 subtraction

๐ŸŽฏ What You Will Learn

Count back
Start with the first number and count backward when the amount being subtracted is small.
Subtract to 10
Break apart the number being subtracted so you can land on 10 first.
Count on
When two numbers are close, count up from the smaller number to find the difference.
Think addition
Use a known addition fact to help find a subtraction fact.
For parents & teachers — standards alignment: This lesson addresses the subtraction-strategy component of CCSS 1.OA.C.6. That standard includes decomposing a number to reach 10 (for example, 13 − 4 = 13 − 3 − 1 = 10 − 1 = 9) and using the relationship between addition and subtraction. The lesson also supports CCSS 1.OA.C.5 by connecting counting with subtraction and CCSS 1.OA.B.4 by treating subtraction as an unknown-addend problem.

๐Ÿง  Key Vocabulary

difference — the result of subtraction.
count back — start at a number and count backward to subtract.
subtract to 10 — break apart the amount being subtracted so you can reach 10 first.
decompose — break a number into smaller parts.
count on — count forward from the smaller number to find the distance to the larger number.
think addition — use a related addition fact to help solve a subtraction problem.

๐Ÿ› ️ Three Useful Subtraction Moves

๐Ÿ‘ฃCount back

Start with the first number and count backward a small number of steps.

๐Ÿ”ŸSubtract to 10

Break apart the number being subtracted so you can land on 10 first.

➕Think addition

Ask what number can be added to the smaller number to reach the larger number.

Scope note: This lesson introduces several useful subtraction strategies. The later Fact Families lesson will explore related addition and subtraction equations more systematically, and the later Word Problems lesson will apply these ideas to a wider range of story situations.

๐Ÿ‘ฃ Strategy 1: Count Back

Counting back is useful when the amount being subtracted is small. For 12 − 3, start at 12 and count back three numbers: 11, 10, 9.

๐Ÿ”Ÿ Strategy 2: Subtract to 10

Ten can be a helpful stopping point. To solve 13 − 4, first subtract 3 to reach 10. There is still 1 more to subtract: 13 − 4 = 13 − 3 − 1 = 10 − 1 = 9.

Common mistake: If 4 is broken into 3 and 1, subtract only those two parts. Do not subtract 3 and then subtract all 4 again.

➕ Strategy 3: Think Addition

Sometimes subtraction is easier when you ask a related addition question. For 14 − 8, ask: 8 + what number = 14? Since 8 + 6 = 14, the difference is 6.

Another useful choice: When two numbers are close, you can count on from the smaller number. For 13 − 11, count 12, 13. The difference is 2.

๐ŸŒŸ 25 Worked Examples

✏️ Try each problem first. Then tap “Show solution” to compare strategies.
1Count back 1
Find 9 − 1.
✨ Show solution๐Ÿ™ˆ Hide solution

Start at 9 and count back 1: 8. Answer: 9 − 1 = 8.

2Count back 2
Find 8 − 2.
✨ Show solution๐Ÿ™ˆ Hide solution

Start at 8 and count back two numbers: 7, 6. Answer: 8 − 2 = 6.

3Count back 3
Find 12 − 3.
✨ Show solution๐Ÿ™ˆ Hide solution

Start at 12 and count back three numbers: 11, 10, 9. Answer: 12 − 3 = 9.

4Choose counting back
Find 14 − 2.
✨ Show solution๐Ÿ™ˆ Hide solution

Because only 2 is being subtracted, counting back is efficient: 14 → 13 → 12. Answer: 14 − 2 = 12.

5Subtract to 10
Find 13 − 4.
✨ Show solution๐Ÿ™ˆ Hide solution

First subtract 3 to reach 10. One more still needs to be subtracted. So 13 − 4 = 13 − 3 − 1 = 10 − 1 = 9. Answer: 9.

6Bridge through 10
Find 15 − 7.
✨ Show solution๐Ÿ™ˆ Hide solution

Subtract 5 to reach 10. That uses 5 of the 7, so 2 more must be subtracted. Then 10 − 2 = 8. Answer: 15 − 7 = 8.

7Subtract 6 from 14
Find 14 − 6.
✨ Show solution๐Ÿ™ˆ Hide solution

Subtract 4 to reach 10. Two more must be subtracted. Then 10 − 2 = 8. Answer: 14 − 6 = 8.

8Subtract 8 from 16
Find 16 − 8.
✨ Show solution๐Ÿ™ˆ Hide solution

Subtract 6 to reach 10. Two more must be subtracted. Then 10 − 2 = 8. Answer: 16 − 8 = 8.

9Subtract 9 from 17
Find 17 − 9.
✨ Show solution๐Ÿ™ˆ Hide solution

Subtract 7 to reach 10. Two more must be subtracted. Then 10 − 2 = 8. Answer: 17 − 9 = 8.

10Subtract 5 from 12
Find 12 − 5.
✨ Show solution๐Ÿ™ˆ Hide solution

Subtract 2 to reach 10. Three more must be subtracted. Then 10 − 3 = 7. Answer: 12 − 5 = 7.

11Subtract 9 from 18
Find 18 − 9.
✨ Show solution๐Ÿ™ˆ Hide solution

Subtract 8 to reach 10. One more must be subtracted. Then 10 − 1 = 9. Answer: 18 − 9 = 9.

12Subtract 3 from 11
Find 11 − 3.
✨ Show solution๐Ÿ™ˆ Hide solution

Subtract 1 to reach 10. Two more must be subtracted. Then 10 − 2 = 8. Answer: 11 − 3 = 8.

13Count on to find the difference
Find 13 − 11.
✨ Show solution๐Ÿ™ˆ Hide solution

Count on from 11 to 13: 12, 13. That is 2 steps. Answer: 13 − 11 = 2.

14Another count-on difference
Find 16 − 13.
✨ Show solution๐Ÿ™ˆ Hide solution

Count on from 13 to 16: 14, 15, 16. That is 3 steps. Answer: 16 − 13 = 3.

15Count on across 10
Find 15 − 9.
✨ Show solution๐Ÿ™ˆ Hide solution

From 9 to 10 is 1 step. From 10 to 15 is 5 more steps. Altogether that is 6. Answer: 15 − 9 = 6.

16Think addition
Find 14 − 8.
✨ Show solution๐Ÿ™ˆ Hide solution

Ask: 8 plus what number makes 14? Since 8 + 6 = 14, 14 − 8 = 6.

17Use a known addition fact
Find 12 − 7.
✨ Show solution๐Ÿ™ˆ Hide solution

Think about the related addition fact: 7 + 5 = 12. Therefore 12 − 7 = 5.

18Think addition for a small difference
Find 17 − 15.
✨ Show solution๐Ÿ™ˆ Hide solution

Ask: 15 plus what makes 17? 15 + 2 = 17. Answer: 17 − 15 = 2.

19Choose an efficient strategy
Which is especially efficient for 13 − 2: count back or subtract to 10?
✨ Show solution๐Ÿ™ˆ Hide solution

Count back is especially efficient because only two steps are needed: 12, 11. Answer: count back; 13 − 2 = 11.

20Choose a strategy near 10
Which is especially useful for 14 − 6: count back one-by-one or subtract to 10?
✨ Show solution๐Ÿ™ˆ Hide solution

Subtracting to 10 makes the work organized: subtract 4 to reach 10, then subtract 2 more. Answer: subtract to 10; 14 − 6 = 8.

21Explain the decomposition
To solve 13 − 5 by subtracting to 10, how should 5 be broken apart?
✨ Show solution๐Ÿ™ˆ Hide solution

Thirteen needs 3 subtracted to reach 10. Break 5 into 3 and 2. Then 13 − 3 − 2 = 10 − 2 = 8. Answer: 5 = 3 + 2.

22Spot the mistake
A student writes 15 − 7 = 15 − 5 − 7. What went wrong?
✨ Show solution๐Ÿ™ˆ Hide solution

The student subtracted 5 but did not remove that 5 from the 7. The 7 must be split into 5 and 2. So 15 − 7 = 15 − 5 − 2 = 10 − 2 = 8. Correct answer: 8.

23Compare two strategies
For 12 − 2, which is simpler: count back 2 or break 2 apart to land on 10?
✨ Show solution๐Ÿ™ˆ Hide solution

Counting back 2 is the simplest description: 11, 10. Because the second step lands on 10, this also connects naturally to using 10 as a friendly number. Answer: 12 − 2 = 10.

24Why think addition?
Why can 13 − 9 be solved by asking 9 + ? = 13?
✨ Show solution๐Ÿ™ˆ Hide solution

Subtraction can be understood as finding a missing addend. Since 9 + 4 = 13, 13 − 9 = 4.

25Challenge: bridge through 10
Find 19 − 11 and show a subtract-to-10 strategy.
✨ Show solution๐Ÿ™ˆ Hide solution

Subtract 9 to reach 10. That uses 9 of the 11, so 2 more must be subtracted. Then 10 − 2 = 8. Answer: 19 − 11 = 8.

๐ŸŽฎ Independent Practice — 30 Problems

  1. Find the difference: 8 − 1.
  2. Find the difference: 10 − 2.
  3. Find the difference: 13 − 3.
  4. Find the difference: 15 − 2.
  5. Find the difference: 17 − 3.
  6. Use a subtract-to-10 strategy: 13 − 5.
  7. Use a subtract-to-10 strategy: 14 − 7.
  8. Use a subtract-to-10 strategy: 15 − 8.
  9. Use a subtract-to-10 strategy: 16 − 7.
  10. Use a subtract-to-10 strategy: 17 − 8.
  11. Use a subtract-to-10 strategy: 18 − 9.
  12. Use a subtract-to-10 strategy: 12 − 4.
  13. Use a subtract-to-10 strategy: 11 − 2.
  14. Count on to find the difference: 14 − 12.
  15. Count on to find the difference: 17 − 14.
  16. Count on to find the difference: 16 − 11.
  17. Think addition to find 13 − 8.
  18. Think addition to find 15 − 9.
  19. Think addition to find 18 − 12.
  20. Think addition to find 16 − 7.
  21. Complete the subtract-to-10 step: 14 − 6 = 14 − 4 − □.
  22. Complete the subtract-to-10 step: 13 − 5 = 13 − 3 − □.
  23. Complete the subtract-to-10 step: 17 − 9 = 17 − 7 − □.
  24. Complete the subtract-to-10 step: 12 − 5 = 12 − 2 − □.
  25. True or false: 16 − 8 = 8.
  26. Which split helps solve 15 − 7 by subtracting to 10: 7 = 5 + 2 or 7 = 4 + 3?
  27. How many should be subtracted first from 13 to land on 10?
  28. In 16 − 9, after subtracting 6 to reach 10, how many more must be subtracted?
  29. Explain in one sentence why thinking 8 + ? = 14 can help solve 14 − 8.
  30. Challenge: Find 17 − 9 using a subtract-to-10 strategy.

๐Ÿ† Lesson Test — 15 Questions

  1. Find the difference: 9 − 2.
  2. Find the difference: 14 − 3.
  3. Use a subtract-to-10 strategy to find 13 − 6.
  4. Use a subtract-to-10 strategy to find 15 − 6.
  5. Use a subtract-to-10 strategy to find 16 − 9.
  6. Count on to find the difference: 15 − 13.
  7. Think addition to find 14 − 9.
  8. Complete: 13 − 4 = 13 − 3 − □.
  9. Complete: 18 − 9 = 18 − 8 − □.
  10. To solve 14 − 6 by subtracting to 10, how can 6 be split?
  11. True or false: 17 − 8 = 9.
  12. Fix the mistake: 13 − 5 = 13 − 3 − 5.
  13. Which strategy is especially efficient for 12 − 1: count back or subtract to 10? Find the difference too.
  14. What strategy asks what number can be added to the smaller number to reach the larger number?
  15. Challenge: Find 15 − 8 and show a subtract-to-10 strategy.

๐Ÿ” Complete Answer Key

Answer-key note: Some subtraction problems can be solved correctly in more than one way. The key shows one clear Grade 1 strategy when a strategy is requested.
๐Ÿ”‘ Show practice answer key๐Ÿ™ˆ Hide practice answer key

Practice Answers

1. 7
2. 8
3. 10
4. 13
5. 14
6. 13 − 5 = 13 − 3 − 2 = 10 − 2 = 8
7. 14 − 7 = 14 − 4 − 3 = 10 − 3 = 7
8. 15 − 8 = 15 − 5 − 3 = 10 − 3 = 7
9. 16 − 7 = 16 − 6 − 1 = 10 − 1 = 9
10. 17 − 8 = 17 − 7 − 1 = 10 − 1 = 9
11. 18 − 9 = 18 − 8 − 1 = 10 − 1 = 9
12. 12 − 4 = 12 − 2 − 2 = 10 − 2 = 8
13. 11 − 2 = 11 − 1 − 1 = 10 − 1 = 9
14. 12 → 13 → 14, so the difference is 2.
15. 14 → 15 → 16 → 17, so the difference is 3.
16. 11 → 12 → 13 → 14 → 15 → 16, so the difference is 5.
17. 8 + 5 = 13, so 13 − 8 = 5.
18. 9 + 6 = 15, so 15 − 9 = 6.
19. 12 + 6 = 18, so 18 − 12 = 6.
20. 7 + 9 = 16, so 16 − 7 = 9.
21. 2
22. 2
23. 2
24. 3
25. True
26. 7 = 5 + 2
27. 3
28. 3
29. Because 8 + 6 = 14, the missing addend 6 is also the difference in 14 − 8.
30. 17 − 9 = 17 − 7 − 2 = 10 − 2 = 8
๐Ÿ… Show test answer key๐Ÿ™ˆ Hide test answer key

Test Answers

1. 7
2. 11
3. 13 − 6 = 13 − 3 − 3 = 10 − 3 = 7
4. 15 − 6 = 15 − 5 − 1 = 10 − 1 = 9
5. 16 − 9 = 16 − 6 − 3 = 10 − 3 = 7
6. 13 → 14 → 15, so the difference is 2.
7. 9 + 5 = 14, so 14 − 9 = 5.
8. 1
9. 1
10. 6 = 4 + 2
11. True
12. 13 − 5 = 13 − 3 − 2 = 10 − 2 = 8.
13. Count back; 12 − 1 = 11.
14. Think addition (find the missing addend).
15. 15 − 8 = 15 − 5 − 3 = 10 − 3 = 7.

๐Ÿ’ก Common Mistakes to Watch For

Counting the starting number as a step
For 12 − 3, the three count-back numbers are 11, 10, and 9.
Subtracting too much when decomposing
If 6 is split into 4 and 2, subtract 4 and then 2 — not 4 and then all 6.
Forgetting what remains after reaching 10
Reaching 10 may be only the first step. Subtract the leftover part too.
Using the same strategy every time
Count back for a small subtraction, use 10 when it creates an easy bridge, or think addition when the numbers are close or a related fact is known.
For parents & teachers — Texas connection: TEKS 1.3(D) expects students to apply basic fact strategies to add and subtract within 20, including making 10 and decomposing a number leading to a 10. TEKS 1.3(E) asks students to explain addition and subtraction strategies up to 20 using spoken words, objects, pictorial models, and number sentences. This lesson develops those expectations on the subtraction side.

๐Ÿ”— Related Lessons

Lesson 9 — Addition Strategies Within 20
Compare make-10 reasoning in addition with subtract-to-10 reasoning here. Lesson 7 — Understanding Subtraction Within 10
Review the meaning of subtraction before using more advanced strategies.

๐Ÿ–จ️ Printable Companion

A free Subtraction Strategies Within 20 Practice Pack will be connected here as the MathLattice printable library grows. It will include count-back practice, subtract-to-10 models, number paths, strategy choice, error analysis, mixed practice, and an answer key.

← Lesson 9: Addition Strategies Within 20 Grade 1 Math Hub Next: Doubles, Near Doubles & Easier Facts →

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