Countdown is a popular television game show in the United Kingdom, shown weekday afternoons on Channel 4. As part of the game, contestants have to solve the following number problem.
Label a set of 24 cards with the numbers in the set {1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 25, 50, 75, 100}. Place the cards randomly on a board with the four large numbers placed on the top row of the board and the remaining numbers placed anywhere on the remaining three rows of the board (all cards must be placed face down).
Choose six numbers from the board (there is no restriction on how many large numbers may be chosen).
Choose a target randomly between 100 and 999 (done by a computer).
Use the six chosen numbers to arithmetically calculate the chosen target. Each number may be used at most once, only the four arithmetic operations +, -, × and ÷ may be used, and no fractions may be introduced into the calculation.
Once the problem has been set, contestants are given 30 seconds to find a solution, and points are awarded according to how close to the target their calculation is.
Implementation
Here is a Macromedia Flash implementation of the Countdown Numbers Game. You may choose the numbers randomly or manually, choose a target randomly or manually, and you may verify your solution using a special calculator (in which pressing 'equals' generates a new number) or have the computer attempt to find a solution. Note: the solver uses ActionScript and is quite slow compared to other solvers.