Subtraction Within 20 — Answer Key
Part A: Fill in the Missing Number
Write the missing number to complete each subtraction sentence.
1. 18 - 7 = 11
Since 18 - ___ = 11, the missing number is 18 - 11 = 7.
2. 15 - 9 = 6
Since ___ - 9 = 6, the missing number is 9 + 6 = 15.
3. Start at 20. Count back 8. You land on 12.
Starting at 20 and counting back 8 lands on 12.
4. 17 - 9 = 8
Since 17 - ___ = 8, the missing number is 17 - 8 = 9.
5. 13 - 5 = 8
Since ___ - 5 = 8, the missing number is 5 + 8 = 13.
6. If 6 + 7 = 13, then 13 - 7 = 6.
This uses the fact family relationship. Since 6 + 7 = 13, then 13 - 7 = 6.
7. If 8 + 9 = 17, then 17 - 9 = 8.
This uses the fact family relationship. Since 8 + 9 = 17, then 17 - 9 = 8.
8. Start at 16. Count back 9. You land on 7.
Starting at 16 and counting back 9 lands on 7.
9. If 5 + 9 = 14, then 14 - 9 = 5.
This uses the fact family relationship. Since 5 + 9 = 14, then 14 - 9 = 5.
Part B: Match the Problem to Its Answer
Draw a line from each subtraction problem to its correct answer.
1. Match each subtraction problem to its answer.
17 - 6
→ 11
14
20 - 8
→ 12
6
13 - 7
→ 6
11
19 - 5
→ 14
12
Match each subtraction to its difference: 17 - 6 = 11, 20 - 8 = 12, 13 - 7 = 6, 19 - 5 = 14.