Halve

a hundred suspects. seven questions. always.

find 1-of-100 — each guess halves the world

Guessing the midpoint and halving the range every time finds any number from 1 to 100 in at most seven tries, against an average of fifty guesses one at a time. It's binary search, felt as a hand motion.

Concepts: binary-search, information.

An interactive you play with one thumb, on Wundr.