7 problems
Brainteasers interview questions
Logic and estimation puzzles with a clean insight at the centre. Stated out loud, usually with no paper, and scored on how you search rather than whether you already knew it.
Two ropes, forty five minutes
Warm-upTwo ropes each burn for exactly one hour but not at a uniform rate. Using only these, measure forty five minutes.
One hundred prisoners and one hundred boxes
HardOne hundred prisoners must each find their own number among one hundred boxes, opening at most fifty each, with no communication. All must succeed. What strategy beats 2^-100?
One thousand bottles, one poisoned
StandardOne of one thousand bottles is poisoned, and the poison acts in exactly one day. How many testers do you need to identify the bottle in a single day?
The blue-eyed islanders
HardOn an island everyone sees others' eye colour but not their own, and anyone who deduces theirs is blue must leave that night. A visitor says aloud 'at least one of you has blue eyes'. With one hundred blue-eyed islanders, what happens?
Estimate the piano tuners
StandardHow many piano tuners work in New York City?
Twelve balls, three weighings
HardTwelve identical-looking balls, one of which differs in weight, and a balance scale. Find the odd ball and whether it is heavy or light in three weighings.
Ants on a pole
StandardAnts are placed at random points on a one-metre pole, each facing a random direction, all walking at one metre per minute. When two meet they reverse. How long until the pole is clear?