Addition Within 20 — Answer Key
Part A: Add Using the Number Line
Start at the first number and count on. Write each sum.
3
+2
5
4
+3
7
5
+4
9
2
+6
8
1
+7
8
6
+4
10
3
+5
8
7
+3
10
Part B: Fill in the Blank
Read each sentence. Write the missing number on the line.
1. 2 + 5 = 7
Start at 2 on the number line and jump 5 spaces to land on 7.
2. 4 + 4 = 8
To find the missing number, subtract 4 from 8: 8 - 4 = 4, so 4 + 4 = 8.
3. If you start at 3 on the number line and jump 6, you land on 9.
Start at 3 on the number line and count 6 jumps forward to land on 9.
4. 6 + 3 = 9
Start at 6 on the number line and jump 3 spaces to land on 9.
5. 5 + 5 = 10
To find the missing number, subtract 5 from 10: 10 - 5 = 5, so 5 + 5 = 10.
Part C: True or False
Write True or False for each statement.
1. 3 + 4 is the same as 4 + 3.
True False
This is true because you can add numbers in any order and still get the same answer: both equal 7.
2. 5 + 5 = 11.
True False
This is false because 5 + 5 = 10, not 11.
3. When you add 0 to any number, the answer is that number.
True False
This is true because adding zero does not change the number.