I learned this at a SECME teacher training. "Didja" is pronounced slurred to sound like "digit." It's a variation on Master Mind, and a great way fill a few minutes before the bell rings.
The object of the game is to guess the secret four digit number. There are no repeated digits (0 – 9) in the number. Once you have guessed, a code will be shown that indicates how successful your guess was. An x mark (x) indicates you have a wrong digit. A dash (-) indicates that you have a correct digit but in the wrong place. A checkmark (√) indicates that you have a correct digit in the correct place. Through a process of elimination, you should deduce the secret number.
For example:
Round 1
4 3 2 1
- x - x
Round 2 (we know the number must have 2 and 4; 4 is not in the first position; 2 is not the third position)
5 6 4 2
x - - -
Round 3 (we know it must have 2, 4, and 6; 4 is not in the first or third position; 2 is not in the third or fourth position; 6 is not in second position)
7 2 4 6
x - - -
Round 4
2 4 6 8
√ √ √ √
Didja guess it?
