One person holds a secret — a number, an app, a device somewhere in the school — and the room gets twenty yes/no questions to corner it. Twenty sounds stingy until you notice what a good question does: it cuts the world of possibilities in half. Twenty honest halvings can find one thing among a million. That halving instinct is the seed of binary search, and you will meet it again with a keyboard in Guess My Number.
How to run it
- The keeper writes the secret down first — no quiet revising later.
- Questions must be answerable yes or no. “What colour is it?” gets sent back for repairs.
- Tally every question on the board. The count is the score.
- After the reveal, replay the game: which questions halved the field, and which barely nibbled at it?
One variation
Secret number between 1 and 1000, and a promise: seven questions are enough, every time. Let the room discover which seven — the halving strategy is more fun found than told.
Guesses are expensive
“Is it a phone?” spends a whole question on one possibility. “Does it have a screen?” interrogates thousands at once. Watch for the moment the room stops guessing and starts narrowing.
Curriculum connection
C1.2
describe simple algorithms that are encountered in everyday situations
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