Addition Within 20 — Answer Key
Part A: Fill in the Missing Number
Use the number line to find the missing number. Write it on the line.
1. Start at 7. Count on 5 more. You land on 12.
Start at 7 on the number line and count 5 jumps forward to land on 12.
2. Start at 9. Count on 4 more. You land on 13.
Start at 9 on the number line and count 4 jumps forward to land on 13.
3. 6 + 8 = 14
To find the missing number, subtract 6 from 14: 14 - 6 = 8, so 6 + 8 = 14.
4. 7 + 8 = 15
To find the missing number, subtract 8 from 15: 15 - 8 = 7, so 7 + 8 = 15.
5. 9 + 8 = 17
To find the missing number, subtract 9 from 17: 17 - 9 = 8, so 9 + 8 = 17.
6. 7 + 6 = 13
To find the missing number, subtract 6 from 13: 13 - 6 = 7, so 7 + 6 = 13.
7. 10 + 8 = 18
To find the missing number, subtract 10 from 18: 18 - 10 = 8, so 10 + 8 = 18.
8. 5 + 7 = 12
To find the missing number, subtract 5 from 12: 12 - 5 = 7, so 5 + 7 = 12.
9. 7 + 9 = 16
To find the missing number, subtract 9 from 16: 16 - 9 = 7, so 7 + 9 = 16.
Part B: Match the Problem to Its Sum
Draw a line from each addition problem to its correct sum.
1. Match each addition problem to its sum.
7 + 6
→ 13
16
9 + 5
→ 14
14
8 + 8
→ 16
13
12 + 6
→ 18
18
Match each addition to its sum: 7 + 6 = 13, 9 + 5 = 14, 8 + 8 = 16, 12 + 6 = 18.