🔢 MathLevel 1Lesson 11
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Understanding Fact Families

Lesson preview: the Mini Lesson and Vocabulary are open to everyone. Guided practice, exercises, the parent checklist and the printable PDF worksheet come with full access (free 7-day trial or membership).

Learning Objectives

  • 1Identify the three numbers in a fact family
  • 2Write all four related facts (two addition, two subtraction)
  • 3Match an addition or subtraction fact to its family partner
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Mini Lesson

A fact family is a group of four math sentences that all use the same three numbers. They show how addition and subtraction are connected!

The three numbers

  • Every fact family uses exactly three numbers.
  • Example: the numbers 3, 5, and 8 form a family.
  • The largest number is always the sum — and always the starting number in subtraction.

The four facts

  • 3 + 5 = 8 (add in one order)
  • 5 + 3 = 8 (add in the other order)
  • 8 − 3 = 5 (subtract one part)
  • 8 − 5 = 3 (subtract the other part)

How to find a family partner

  • Look at the three numbers in the fact you are given.
  • Use those same three numbers to write the partner fact.
  • Example: if you know 4 + 7 = 11, the subtraction partners are 11 − 4 = 7 and 11 − 7 = 4.
Fact family house for the numbers 3, 5, and 8A house shape. The roof triangle holds 8. Two circles on the base hold 3 and 5. Below: four facts — 3 plus 5 equals 8, 5 plus 3 equals 8, 8 minus 3 equals 5, 8 minus 5 equals 3.Fact Family House8sum35partpartAddition facts3 + 5 = 85 + 3 = 8(swap the parts!)Subtraction facts8 − 3 = 58 − 5 = 3(start with the sum!)
A fact family house — the sum (8) sits in the roof, the two parts (3 and 5) in base circles, and all four related facts shown below in two color-coded panels.
Fact family triangle and four facts for 4, 7, and 11A triangle with 11 at the top, 4 bottom-left, 7 bottom-right. Below: four fact cards — 4 plus 7 equals 11, 7 plus 4 equals 11, 11 minus 4 equals 7, 11 minus 7 equals 4.Another Fact Family: 4, 7, 1111474 + 7 = 117 + 4 = 1111 − 4 = 711 − 7 = 4Same 3 numbers — 4 different facts! That's a fact family.
The fact family for 4, 7, and 11 — a three-number triangle at the top and all four facts as labeled cards below.
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Ask yourself: "What are the three numbers? Can I swap them to write another fact?"

Vocabulary
Fact family
A group of four math sentences that use the same three numberse.g. 3, 5, and 8 make one fact family.
Sum
The answer when you add two numberse.g. The sum of 3 and 5 is 8.
Addition
Putting numbers together to find how many altogethere.g. 3 + 5 = 8 is addition.
Subtraction
Taking one number away from another to find how many are lefte.g. 8 − 5 = 3 is subtraction.
Related fact
A math fact that uses the same numbers as another facte.g. 3 + 5 = 8 and 8 − 5 = 3 are related facts.
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