Bulls and cows is a traditional English pencil and paper game for two players whose objective is to guess a four digit secret number. All digits must be different. Nothing else than paper and pencil are needed.
On a sheet of paper one player writes down the secret number.
On another sheet of paper the opponent has to guess the number in different successive tries, each try receives a public evaluation from the owner of the secret number. A right digit on the right place is a bull, a right digit on the wrong place is a cow.
Example:
Secret number: 4271
tries number scores
1 1234 1B2C (1 bull and 2 cows, "2" is bull, "4" and "1" are cows.)
2 5678 1B0C
3 9012 0B2C
4 9087 0B1C
. ...... .......
. ...... .......
8 4271 4B0C
Once the number is guessed the player roles are inverted, the owner of the secret number has to guess and the player who guessed writes down a new secret four digit number. The winner is the player with less tries in finding the right number.
The game can also be played by two teams of 2-3 players, team members share their thoughts before they take a decision.
Instead of a four digit secret number it can be also a 3-6 digit secret number. The more digits, the more difficult is the game.
The game Mastermind is Bulls and Cows without a plastic board and coloured plastic pins.
Wikipedia article about Bulls and Cows
More Paper and pencil games