Adding Three Numbers — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. 7 + 3 + 6. First 7 + 3 = 10. Then 10 + 6 = 16
Rearranging addends to form a ten first is a core Grade 1 strategy that speeds up three-number addition.
2. 2 + 5 + 8. Rearrange: 2 + 8 = 10. 10 + 5 = 15
Pairing 2 and 8 makes ten, which is a friendly number to add onto for any first grader.
3. 4 + 9 + 1. First 9 + 1 = 10. 10 + 4 = 14
Nine and one are a known bond that makes ten, perfect for reordering three-addend sums.
4. 6 + 2 + 4 = 12
Sixes and fours are a ten-bond pair, so reordering speeds up mental math in first grade.
5. 3 + 7 + 5 = 15
Three plus seven is a ten-pair, making the final addition much easier than adding left to right.
6. 8 + 1 + 2 = 11
Reordering to use the eight-and-two pair turns a tricky sum into a simple ten plus one.
7. 5 + 4 + 5 = 14
First graders can spot the doubled 5s and add them first to form ten, then add the middle addend.
8. 9 + 2 + 1 = 12
Adding 9 and 1 first yields ten, and then adding 2 brings the answer quickly and accurately.
9. 3 + 6 + 4 = 13
Putting the ten-bond pair first reduces the chance of miscounting when working with three addends.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
6 + 4 + 3
→ 13
13
8 + 2 + 5
→ 15
15
9 + 1 + 4
→ 14
14
7 + 3 + 2
→ 12
12
Matching three-addend problems to sums builds first graders' eye for ten-bond pairs hidden in addition.