Fact Families: Addition & Subtraction — Answer Key
Part A: Multiple Choice
Circle the correct answer for each question.
1. Which equation belongs to the fact family with 6, 9, and 15?
A) 6 + 8 = 14
B) 15 - 9 = 6
C) 9 - 6 = 3
D) 15 + 6 = 21
The fact family for 6, 9, and 15 includes 6 + 9 = 15, 9 + 6 = 15, 15 - 6 = 9, and 15 - 9 = 6. Only "15 - 9 = 6" is one of these equations.
2. If 8 + 7 = 15, which equation is also in the same fact family?
A) 15 - 8 = 6
B) 7 + 8 = 16
C) 15 - 7 = 8
D) 8 + 8 = 15
The fact family for 7, 8, and 15 includes 15 - 7 = 8. The other options use incorrect numbers or results.
3. Which three numbers form a fact family?
A) 4, 5, 8
B) 6, 7, 14
C) 5, 9, 14
D) 3, 8, 10
5 + 9 = 14, so the numbers 5, 9, and 14 form a valid fact family. The other sets do not add up correctly.
4. Anna knows 9 + 8 = 17. Which related fact can she use to check her work?
A) 17 + 8 = 25
B) 17 - 9 = 8
C) 9 - 8 = 1
D) 8 + 9 = 18
Since 9 + 8 = 17, Anna can check by subtracting: 17 - 9 = 8. This is the inverse operation in the same fact family.
Part B: Fill in the Missing Number
Use what you know about fact families to find each missing number.
1. 7 + 9 = 16, so 16 - 7 = 9.
In the fact family for 7, 9, and 16, 7 + 9 = 16 and 16 - 7 = 9. Both blanks are 9.
2. If 8 + 9 = 17, then 17 - 9 = 8.
Since 8 + 9 = 17, subtracting 9 from 17 gives back 8: 17 - 9 = 8.
3. The missing number: 20 - 7 = 13.
20 - 7 = 13, so the missing number is 7. This belongs to the fact family for 7, 13, and 20.
4. 6 + 12 = 18, using the fact family for 6, 12, and 18.
In the fact family for 6, 12, and 18, 6 + 12 = 18, so the missing number is 12.
5. If 5 + 9 = 14, then 14 - 5 = 9.
Since 5 + 9 = 14, the inverse subtraction is 14 - 5 = 9. The missing number is 14.