Fact Families: Addition & Subtraction — Answer Key
Part A: Multiple Choice
Circle the correct answer for each question.
1. Which equation is NOT in the fact family for 7, 8, and 15?
A) 7 + 8 = 15
B) 15 - 7 = 8
C) 8 + 7 = 15
D) 15 - 6 = 9
The fact family for 7, 8, and 15 only uses the numbers 7, 8, and 15. "15 - 6 = 9" uses 6 and 9, which are not part of this family.
2. How many equations are in every fact family with three different numbers?
A) 2
B) 3
C) 4
D) 5
Every fact family with three different numbers has exactly 4 equations: 2 addition facts and 2 subtraction facts.
3. Liam knows 9 + 7 = 16. Which equation can he write from the same fact family?
A) 16 - 3 = 13
B) 16 - 9 = 7
C) 9 + 6 = 15
D) 16 + 7 = 23
Since 9 + 7 = 16, Liam can write the inverse: 16 - 9 = 7. This uses the same three numbers 7, 9, and 16.
4. Which fact family includes the equation 20 - 11 = 9?
A) 9, 10, 19
B) 9, 11, 20
C) 11, 9, 21
D) 9, 12, 20
20 - 11 = 9 uses the numbers 9, 11, and 20. Since 9 + 11 = 20, these three numbers form the correct fact family.
Part B: Fill in the Missing Number
Use fact family relationships to find each missing number.
1. If 9 + 9 = 18, then 18 - 9 = 9.
Since 9 + 9 = 18, subtracting 9 from 18 gives back 9: 18 - 9 = 9. This is a doubles fact family.
2. 12 + 8 = 20, so 20 - 8 = 12.
In the fact family for 8, 12, and 20, 12 + 8 = 20 and 20 - 8 = 12. Both blanks are 12.
3. The fact family for 7, 9, and 16 uses 16 - 7 = 9.
Since 16 - 7 = 9, the missing number is 9. The fact family is 7, 9, and 16.
4. 19 - 9 = 10, so 10 + 9 = 19.
19 - 9 = 10 and 10 + 9 = 19. The first blank is 9 and the second blank is 19, from the fact family 9, 10, and 19.
5. If 6 + 14 = 20, then 20 - 14 = 6.
Since 6 + 14 = 20, the inverse subtraction gives 20 - 14 = 6.