A mathematical problem in which a set of deliveries must be made along a set of available routes between fixed sources and destinations, within limited time periods, and with the possibility of changing vehicles during a trip.

A particularly complex or challenging problem or puzzle.

Alternative form of measurement problem

A brainteaser regarding probability, in which a game show contestant picks a door to win a prize. One door conceals a car; the other two conceal goats. After the contestant picks a door, the host opens one of the two remaining doors which reveals a goat. Counterintuitively, it is then in the contestant's interests to switch to the remaining door.

A conspiracy theory postulated by David Icke in which the government (or another higher power) manipulates the population by introducing a problem and then using their own means to solve that problem.

(astronomy) The problem of calculating the motion of three celestial bodies that interact with each other gravitationally

A geometric puzzle involving calculating the width of an alley based on the height at which two ladders cross when propped diagonally across it.

(economics) The situation where those who benefit from goods or resources do not pay for them, resulting in a lack of funding and subsequent underprovision.

(mathematics) A problem in combinatorics, in which 15 schoolgirls go walking three abreast for seven days in succession, and must be arranged so that no two walk abreast more than once.

plural of principal-agent problem