Concept 4 of 6
Subtracting Within 20: Count Back
Today's big idea
To subtract, count back one for each you take away.
13 − 5: hop back 12, 11, 10, 9, 8.
How it works
👀 What's going on?
You had 13 balloons and 5 popped. How many are left?
💡 Here's the trick
To subtract, start at the number and count back one for each you take away.
13 − 5: count back 12, 11, 10, 9, 8. You land on 8.
✍️ Try it
15 − 6: count back 6 steps. → 9.
⚠️ Watch out
Count back exactly one number for each one you take away, no more.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“What is 14 − 6?”
- 1
Start at 14
Hold 14 and get ready to count back. ✋
- 2
Count back six
14 → 13 → 12 → 11 → 10 → 9 → 8
- 3
Answer ✓
14 − 6 = 8
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Start at 13 and tap to count back 5.
13 − 5
13
taken away 0 of 5
Quick check
✅ VERIFICATION
What is 12 − 4?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Fact Families
Three numbers make two adds and two subtracts.