A NUMBER IN THE DARK
Five lanterns. One quiet thought.
Choose a whole number from 1 to 31. Keep it to yourself. We’ll follow a little light and see where it leads.
Have a number in mind?
At each lantern, tell me whether your number is in the group. Keep the same number for all five choices. You never need to type it.
- Lantern 1
- Lantern 2
- Lantern 3
- Lantern 4
- Lantern 5
Is your number here?
Read the whole group, then choose yes or no.
The light leads to…
Curious? Show me how the lanterns work.
Five small pieces make a number.
The lanterns stand for 1, 2, 4, 8, and 16. Each group contains exactly the numbers that use its value in binary. Every whole number from 1 to 31 has one unique combination.
We add the values of the lanterns where you said yes. For 19, that is 1 + 2 + 16. Five yes-or-no answers carry enough information to identify your number—no mind reading needed.
This presentation uses the traditional binary-number-card principle. STEMAZing’s Binary Mathemagic lesson (PDF, opens a new tab) teaches the mathematics. Our paper-card lesson turns it into a performance.
Another thought to keep?
Leave the lanterns behind and let a card find its way home.
Try the 21-card trick →