Think of a number — Maths trick for kids

The trick

Undo the steps — “to find the start number, undo each step from the last to the first”

1. Going forwards: do the steps in order.
2. Going backwards: start from the result and undo each step, last one first.
3. Undo + with −, × with ÷, and doubling with halving.

Use it for: Magic tricks for family and friends, and solving “I think of a number” puzzles in school tests.

Worked example: I thought of a number, multiplied it by 3 and added 4. I got 25. What was my number? → 7

✏️ Practice

Work it out in your head or on paper, then tap your answer — or type it and press Check. Stuck? Press “Show me how”.

🏁 Trick 6 test

20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.

🏅 Sign in with Google to earn the 🔮 Mind Reader badge when you pass — and a certificate when you finish all 5 tricks of Part 2 · Number magic. You can still take the test without signing in.

🖨️ Think of a Number Puzzles Worksheet

• Worksheet set 1 (PDF)
• Worksheet set 2 (PDF)
• Worksheet set 3 (PDF)