Level 2 · Performance Magic
Leapfrog Addition
Ask someone to write down two numbers. Build a sequence of 10 by Fibonacci rules. Then announce the sum of all 10 — before they finish adding.
How to Perform It
- Ask a volunteer to write any two numbers (you can even have them choose).
- Have them generate 10 terms: each new term = the sum of the previous two.
- While they write, glance at the 7th term.
- Multiply it by 11 (using the Elevens Trick!) — that's your prediction.
- Announce the total before they finish summing all 10.
Worked Example
Starting numbers: 3 and 7
3, 7, 10, 17, 27, 44, 71, 115, 186, 301
7th term = 71. Prediction: 71 × 11 = 781
Actual sum: 3+7+10+17+27+44+71+115+186+301 = 781 ✓
Why It Works
Call the two starting numbers a and b. The 10 terms are: a, b, a+b, a+2b, 2a+3b, 3a+5b, 5a+8b, 8a+13b, 13a+21b, 21a+34b. Their sum is 55a + 88b = 11(5a + 8b) — which is exactly 11 times the 7th term.
💡 Teaching Tip
This trick beautifully combines two skills from earlier in the curriculum: Fibonacci sequences (a pattern recognition skill) and the Elevens Trick (multiplying by 11). Use it to show how tricks build on each other.