They each right their estimation on their card.
Students place the cards in order from least to greatest.
They wager on which answer they think is correct.
Then they check their answer.
The person closest to the right answer without going over wins. One of the students is designated the banker and will pay out the winnings based on the odds. There is really endless possibilities for this game. I created ones where students estimate logs, angle measures, equations, fractions, square roots, ect. Here is the link to all of my games so far. I have a classroom set of iPads, so I just have students open the file in iBooks and then flip through each slide. You could easily project the slides on the board and have everyone go at the same pace or just print them out. I created the game board using a manila folder and just laminating all of the pieces so students can use dry erase markers. I think the game works best with 5-6 per group, this way you get a wide range of answers. It might be useful to limit the time a student has to answer so their responses are actual estimations and not a precise calculation. Here are the files to all the game pieces:Game Board, Game Pieces 1, Game Pieces 2, Game Tokens