Themes · wave 1

Codes and Winning Strategies

Clever counting turns into tricks, codes and strategies. Each gem here is a game first and an idea second.

Gems

An old puzzle of rings on a bar hides a way of counting where every step changes just one digit.

Five cards read any number from 0 to 31. Seven cleverer cards still find your number when you lie about one of them.

One of 240 test tubes is poisoned. You have 8 mice and a single day. Binary numbers find the tube.

Any two cards in Dobble share exactly one symbol. Here is how to build such a deck, using geometry where parallel lines do not exist.

Everyone ranks everyone in the other group. Can you pair them up so that no two people would rather run off together?

Ants march along a stick and turn round whenever they meet. How long until every ant has fallen off? One idea makes it easy.

You have the map but cannot see the robot. Is there one list of commands that leads it out from every possible starting cell?

Two players take turns sliding a queen towards the corner, and whoever gets her there wins. The safe squares follow the golden ratio.

A heap of 100 keys for 100 identical locks. Key by key takes 4,950 tries at worst. Can any cleverer method promise fewer?