Addition within 20 — Answer Key
Part A: Solve the Addition Problems
Add the numbers. Write the answer on the line.
5
+5
10
6
+6
12
7
+7
14
8
+8
16
9
+9
18
10
+10
20
5
+6
11
6
+7
13
7
+8
15
8
+9
17
9
+10
19
4
+5
9
Part B: Fill in the Missing Number
Write the missing number to complete each number sentence.
1. 6 + 6 = 12
6 + 6 = 12. This is the doubles fact for 6.
2. 7 + 7 = 14
7 + 7 = 14. This is the doubles fact for 7.
3. 8 + 8 = 16
8 + 8 = 16. This is the doubles fact for 8.
4. 10 + 5 = 15
10 + 5 = 15. The missing addend is 5.
5. 9 + 9 = 18
9 + 9 = 18. This is the doubles fact for 9.
6. 10 + 10 = 20
10 + 10 = 20. The missing addend is 10.