Fact Families: Addition & Subtraction — Answer Key
Part A: Complete the Fact Family Equations
Solve each equation. Write the answer on the line.
5
+8
13
8
+5
13
13
-5
8
13
-8
5
6
+9
15
9
+6
15
15
-6
9
15
-9
6
Part B: Fill in the Missing Number
Read each sentence. Write the missing number on the line.
1. If 5 + 8 = 13, then 13 - 8 = 5.
Since 5 + 8 = 13, the inverse subtraction gives 13 - 8 = 5.
2. The numbers 6, 9, and 15 form a fact family.
6 + 9 = 15, so the numbers 6, 9, and 15 form a fact family.
3. If 9 + 6 = 15, then 15 - 9 = 6.
Since 9 + 6 = 15, subtracting 9 from 15 gives back 6: 15 - 9 = 6.
4. 8 + 5 = 13, so 13 - 5 = 8.
Since 8 + 5 = 13, subtracting 5 from 13 gives back 8: 13 - 5 = 8.
5. The fact family for 5, 8, and 13 has 4 equations.
Every fact family with 3 different numbers has 4 equations: 2 addition and 2 subtraction.
Part C: True or False
Read each statement. Write True or False.
1. 5 + 8 = 13 and 13 - 5 = 8 are in the same fact family.
True False
True — these two equations use the same three numbers 5, 8, and 13.
2. The numbers 6, 8, and 15 form a fact family.
True False
False — 6 + 8 = 14, not 15, so these three numbers do not form a fact family.
3. If you know 9 + 6 = 15, you also know 15 - 9 = 6.
True False
True — addition and subtraction are inverse operations, so knowing 9 + 6 = 15 means 15 - 9 = 6.