Originally posted by Mouse2
the second doesn't work. it always guesses a single-digit number (unless it is temporarily messed up for some reason)
That's what it is supposed to do.
1) Choose a 4-digit number, eg. 9433
2) Rearrange its digits to make a another 4-digit mumber, 3934
3) Subtract the smaller number from the larger. 9433 - 3934 = 5499
4) Circle one of the digits of the resulting number. (But not '0' 'cos that's already a circle.) eg. circle '5'
5) Input into the computer the remaing 3 digits. Here, these are '4', '9', and '9'.
6) The computer will now read your mind and output which number you circled, but only if you concentrate real hard on that number.