Math · Stage 1
Find the starting number by undoing each step, then verify forwards
Run the steps in reverse to travel back to where you began — then redo them going forwards to be sure.
✦ Math📘 Stage 1 · S1⏱ ~9 min🧒 Ages 5–6★ Free to start
I can find the starting number by undoing each step in reverse, then verify by redoing forwards.
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Kavi's Secret-Number Machine 🤖
"I fed a secret number into my machine," giggled Kavi. "It added 2, then added 3, and out popped 10! Can you find my secret number?" To travel back to the start, Kavi runs the steps in reverse — take away 3, then take away 2. "And to be sure, I'll redo them forwards. If I land on 10 again, I know I'm right!"
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What your child will learn
1The result is your start + everything addedKavi's machine turned a secret start into 10 by adding 2 then 3 — that is 5 added in all. A number bond shows it: the whole (10) is made of your start and the 5 the machine added. Slide the bond to see start + added = 10.
2Check it by hopping forwardsOnce you think you have found the start, redo the steps going forwards to be sure. Start at your number and hop along the line — if you land exactly on the result, your answer is right.
3Know your bonds, undo in a flashEvery start + added = result is a number bond you already know. If you know 4 + 6 = 10, then a puzzle that adds 6 and ends on 10 is instant — the start was 4.
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A peek inside
Kavi's machine adds 2, then adds 3, and shows 10. What was the secret start?
undo in reverse: 10 − 3 = 7, then 7 − 2 = 5 · check forwards: 5 + 2 = 7, 7 + 3 = 10 ✓
Try this at home: Kavi thinks of a number, adds 5, and gets 12. What was the number? (undo, then check)
Ready to play and learn?
Start the free interactive lesson, or print the handout for screen-free play.
Part of Math · Stage 1 · S1 on KAVI Academy — a secular, whole-child learning platform for ages 5–12.