Fact Families (Addition & Subtraction to 20) — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Which set of numbers makes a fact family?
A) 3, 8, 11
B) 4, 7, 13
C) 5, 6, 10
D) 9, 2, 13
A) 3, 8, 11 works because the two smaller numbers, 3 and 8, add up to the largest number, 11. Fact families always follow the rule part + part = whole.
2. Which fact is in the same family as 16 - 9 = 7?
A) 7 + 8 = 15
B) 9 + 7 = 16
C) 16 - 8 = 8
D) 7 + 6 = 13
B) 9 + 7 = 16 uses the same three numbers (7, 9, 16) as the subtraction fact. Adding the two parts together gives back the whole you started with.
3. What is the missing number? 6 + ___ = 13
A) 8
B) 6
C) 7
D) 9
C) 7 is correct because 6 + 7 = 13, or you can subtract 13 - 6 to find the missing part. Using fact family facts makes finding unknowns simple.
4. Which fact family uses the numbers 8, 9, and 17?
A) 8 + 9 = 17 and 17 - 8 = 9
B) 8 + 8 = 16 and 16 - 8 = 8
C) 9 + 9 = 18 and 18 - 9 = 9
D) 7 + 9 = 16 and 16 - 7 = 9
A) 8 + 9 = 17 and 17 - 8 = 9 both use the exact trio 8, 9, and 17. The addition gives the whole, and the subtraction takes one part away to reveal the other.
Part B: Fill in the Blank
Write the correct answer on each line.
1. 5 + 8 = 13
Move 2 from the 5 over to the 8 to make 10, then add the 3 left for a total of 13. The make-ten strategy keeps the numbers easy to manage.
2. 8 + 5 = 13
Flipping the order, 8 + 5 gives the same sum as 5 + 8, which is 13. Both equations belong to the 5, 8, 13 fact family.
3. 13 - 5 = 8
Take the 5 part away from the whole 13 to leave the other part, 8. Subtraction is the inverse of the related 5 + 8 = 13 fact.
4. 13 - 8 = 5
Count up from 8 to 13 (9, 10, 11, 12, 13) to find 5 jumps. So 13 - 8 = 5, the fourth equation in this fact family.
5. 9 + 9 = 18
This is a doubles fact: 9 + 9 = 18, so the missing addend must be 9. Doubles are easy to spot because both parts match.