Gordon Hamilton of Math Pickle posted **Rock – Low unique number game** for grades K–2. If you have a set of active kids and a few minutes to spare, give it a try!

### How to Play Rock

- Everyone makes a rock shape with eyes closed.
- Everyone chooses a number: 0, 1, 2, 3, 4, 5, 6, 7, 8 …
- Teacher calls out numbers consecutively, starting at 0.
- When a student hears their number being called they immediately raise a hand. When the teacher tags the hand, they stand up.
- If more than one hand was raised, those students lose. They become your helpers, tagging raised hands.
- If only one hand was raised, that child wins the round.

“Each game takes about 45 seconds,” Hamilton says. “This is part of the key to its success. Children who have not learned the art of losing are quickly thrown into another game before they have a chance to get sad.”

The experience of mathematics should be profound and beautiful. Too much of the regular K-12 mathematics experience is trite and true. Children deserve tough, beautiful puzzles.

### What Happens When Grownups Play Rock

What are the best numbers to pick? Patrick Vennebush hosted on online version of the game at his Math Jokes 4 Mathy Folks blog a few years back, though we didn’t have to bend over into rocks—which is a good thing for some of us older folks.

Vennebush also posted a finger-game version suitable for small groups of all ages, called **Low-Sham-Bo**:

- On the count of 1-2-3, each person “throws” out a hand showing any number of fingers from zero to five.
- The winner is the person who throws the smallest unique number.

You may want to count “Ready, set, go!” for throwing out fingers, so the numbers in the count don’t influence the play.

The official name for this sort of game is Lowest Unique Bid Auction.