Solution to Riddle of the Week

Solution to Riddle of the Week: Adam & Eve Play Rock-Paper-Scissors

Difficulty level: Moderate

Michael Stillwell
 
By Jay Bennett

Like many logic puzzles, this one might seem impossible to solve at first glance. Adam and Eve could have played their hands in any order, so how can you know how many games each person won? It might not be until you start running through the games and tallying up the wins that the pattern becomes clear.

SOLUTION

Let's look at the played hands again:

• Adam: 3 rock, 6 scissors, 1 paper
• Eve: 2 rock, 4 scissors, 4 paper

The key to solving this riddle is realizing that Adam played scissors six times. Because there were no ties, that means Eve didn't play scissors in any of those six games. Now look at the various hands Eve did play. Because she played scissors four times, and none of those could line up with one of the six times Adam played scissors, she must have played all six of her other hands on Adam's six scissors.

Therefore, six of the games, not necessarily in order, were as follows:

• Adam: scissors vs. Eve: rock [Winner: Eve]
• Adam: scissors vs. Eve: rock [Winner: Eve]
• Adam: scissors vs. Eve: paper [Winner: Adam]
• Adam: scissors vs. Eve: paper [Winner: Adam]
• Adam: scissors vs. Eve: paper [Winner: Adam]
• Adam: scissors vs. Eve: paper [Winner: Adam]

Now look at what is left over. We see that Eve has only scissors left. Therefore, the other four games are:

• Adam: rock vs. Eve: scissors [Winner: Adam]
• Adam: rock vs. Eve: scissors [Winner: Adam]
• Adam: rock vs. Eve: scissors [Winner: Adam]
• Adam: paper vs. Eve: scissors [Winner: Eve]

Tally it all up, and Adam wins, 7 to 3. Watch out for those serpents and come back next week for another riddle!