A puzzle by Yoshinao Katagiri: A boy and a girl played rock paper scissors 10 times. Altogether the boy played rock three times, scissors six times, and paper once, and the girl played rock twice, scissors four times, and paper four times (though, in each case, the order of these plays is unknown). There were no ties. Who won?
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Since there were no ties, each time the boy played scissors the girl must have played rock or paper. The girl’s record shows us that he lost two of those six rounds and won four.
Likewise, in the four rounds in which the girl played scissors, the boy played rock three times and paper once. She lost three times and won once.
Altogether the boy won seven rounds and lost three.
(Via Nobuyuki Yoshigahara’s Puzzles 101: A Puzzlemaster’s Challenge, 2004.)