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 8. Count on 6 more. You land on 14.
Start at 8 on the number line and count 6 jumps forward to land on 14.
2. Start at 5. Count on 7 more. You land on 12.
Start at 5 on the number line and count 7 jumps forward to land on 12.
3. 4 + 9 = 13
To find the missing number, subtract 4 from 13: 13 - 4 = 9, so 4 + 9 = 13.
4. 9 + 7 = 16
To find the missing number, subtract 7 from 16: 16 - 7 = 9, so 9 + 7 = 16.
5. 8 + 12 = 20
To find the missing number, subtract 8 from 20: 20 - 8 = 12, so 8 + 12 = 20.
6. 9 + 5 = 14
To find the missing number, subtract 5 from 14: 14 - 5 = 9, so 9 + 5 = 14.
7. 10 + 7 = 17
To find the missing number, subtract 10 from 17: 17 - 10 = 7, so 10 + 7 = 17.
8. 3 + 8 = 11
To find the missing number, subtract 3 from 11: 11 - 3 = 8, so 3 + 8 = 11.
9. 9 + 6 = 15
To find the missing number, subtract 6 from 15: 15 - 6 = 9, so 9 + 6 = 15.
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.
6 + 9
→ 15
20
7 + 4
→ 11
15
11 + 5
→ 16
16
13 + 7
→ 20
11
Match each addition to its sum: 6 + 9 = 15, 7 + 4 = 11, 11 + 5 = 16, 13 + 7 = 20.