Adding Three Numbers — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. 4 + 4 + 2. Double 4 is 8. 8 + 2 = 10
Doubles are facts first graders know quickly, so adding the extra number after is much easier.
2. 3 + 3 + 5. Double 3 is 6. 6 + 5 = 11
Spotting a double turns a three-addend problem into a simple two-step addition.
3. 5 + 5 + 3. Double 5 is 10. 10 + 3 = 13
Because 5 + 5 is a friendly ten, adding the last number is quick mental math for Grade 1.
4. 2 + 2 + 7 = 11
Finding the doubles pair first keeps the work organized and reduces counting errors.
5. 6 + 6 + 1 = 13
Doubles plus one is a common first-grade strategy that builds fluency with addition facts.
6. 1 + 4 + 4 = 9
The double may not be first — scanning all three addends teaches flexible thinking.
7. 7 + 3 + 3 = 13
Using doubles first keeps the numbers small before adding the bigger addend at the end.
8. 2 + 6 + 6 = 14
Knowing doubles up to 10 + 10 helps first graders tackle three-number sums confidently.
9. 5 + 2 + 5 = 12
Rearranging to add the 5 + 5 double first makes this a friendly ten plus two problem.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
4 + 4 + 1
→ 9
9
3 + 3 + 2
→ 8
8
5 + 5 + 4
→ 14
14
2 + 2 + 6
→ 10
10
Matching near-doubles expressions to sums trains first graders to recognize doubles inside larger problems.