Concept 5 of 6
Fact Families
Today's big idea
Three numbers make two adds and two subtracts.
8, 5 and 13: 8+5, 5+8, 13−8, 13−5.
How it works
👀 What's going on?
8 + 5 = 13. That one fact hides three more.
💡 Here's the trick
The same three numbers make a family: two adds and two subtracts.
From 8, 5 and 13: 8 + 5 = 13, 5 + 8 = 13, 13 − 8 = 5, 13 − 5 = 8.
✍️ Try it
Family of 6, 9 and 15: 6 + 9 = 15, 9 + 6 = 15, 15 − 6 = 9, 15 − 9 = 6.
⚠️ Watch out
The biggest number is the total, so it always goes first in a subtraction.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Write the whole family of 6, 9 and 15.”
- 1
The two adds
6 + 9 = 15 and 9 + 6 = 15.
- 2
The two subtracts
The total 15 goes first: 15 − 6 = 9 and 15 − 9 = 6.
- 3
Answer ✓
6+9=15, 9+6=15, 15−6=9, 15−9=6
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Tap the 4 facts that belong to the family of 4, 7, 11.
Found 0 of 4
Quick check
✅ VERIFICATION
Which fact is NOT in the family of 4, 7 and 11?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Missing Numbers & Adding Three
Subtract to find a gap; add three two at a time.