Adding Three Numbers — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Which number completes 5 + 4 + ___ = 12?
A) 1
B) 2
C) 3
D) 4
Finding the missing addend uses the inverse relationship between addition and subtraction, important in Grade 1.
2. 4 + ___ + 3 = 10. What is the missing number?
A) 2
B) 3
C) 4
D) 5
Adding the two known addends first makes it clear how much more is needed to reach the total.
3. Which number completes 2 + 6 + ___ = 11?
A) 2
B) 3
C) 4
D) 5
Counting up from the partial sum to the target total is a solid first-grade strategy.
4. 7 + 1 + ___ = 10. What number is missing?
A) 1
B) 2
C) 3
D) 4
Knowing ten-bond facts helps first graders quickly spot the missing piece in a three-addend equation.
Part B: Fill in the Blank
Write the correct answer on each line.
1. 3 + 3 + 4 = 10
Adding the two known numbers first reveals the gap the missing addend must fill.
2. 5 + 2 + 3 = 10
First graders use ten-frame thinking to find how many more complete the sum of ten.
3. 3 + 4 + 2 = 9
The missing addend can come first, so students practice flexible placement of unknowns.
4. 6 + 3 + 1 = 10
Combining the known addends first simplifies the search for the unknown number.
5. 2 + 5 + 4 = 11
Counting from 7 to 11 is four steps, which gives the missing addend for this problem.