Odd Coin

📖 Strategy guide: How to solve Odd Coin: count possibilities, split them in three

How to play

Every coin on the desk looks the same, but one of them is a fake. The card above the balance tells you what is known: sometimes that the fake is lighter, sometimes that it is heavier, and sometimes only that it is different. Tap a coin to put it on the left pan, tap it again to move it to the right pan, and once more to put it back in the tray. You can also drag coins. With the same number of coins on each pan, press Weigh. The beam tips toward the heavier side or stays level.

When you are sure, press Name the fake, tap the coin and say whether it is heavier or lighter. Your score is the number of weighings you used, and fewer is better. If another coin still fits every result, you were not sure enough: the game shows you that coin, and the round scores nothing.

Daily, levels and challenges

The daily puzzle is the same for everyone and changes at midnight UTC. It changes the number of coins, what you know about the fake, and whether you get a stamped silver weight that is certainly genuine. Easy has seven to nine coins and tells you which way the fake differs. Hard has twelve or thirteen coins and does not keep track for you: use ✎ to pencil your own marks on the coins. ⚔️ copies a link to the exact puzzle, ↶ strikes out the last weighing and ↻ starts again.

How the puzzles are made

There is no hidden answer to peek at. The fake is decided only by your weighings: each time, the balance gives the result that leaves you the most work, first in weighings still needed and then in coins still in doubt. A solver works out the par, which is the fewest weighings that always succeed, before you start. Guessing cannot beat par. Only a method that works whatever the scale says can match it.

Tips

• Each weighing has three outcomes, so aim to split the possibilities into three equal groups.
• A coin that tipped the scale one way can only be fake in that direction. Mix such coins with fresh ones.
• Coins proven genuine are useful: they fill a pan without adding doubt.

Designed and built by the Eigengames team; every par is computed and checked by our own solver.