Eight-Ball Balance Lab
0 of 2 weighings used

Find one heavier ball in two weighings.

Assign balls to the left or right pan, weigh equal-sized groups, and use the result to narrow the suspects. The hidden heavy ball changes with every new puzzle.

Balance scale

Select a ball repeatedly to cycle it through left pan, right pan, and bench.
Emptyleft pan
Emptyright pan

A valid weighing needs the same nonzero number of balls on each pan.

The optimal decision tree

The balance has three outcomes, so each weighing can transmit one of three pieces of information. Two weighings distinguish up to 3 squared, or 9, states, enough for 8 balls.

Weighing 1

Compare balls 1, 2, 3 against 4, 5, 6.

Left heavy: suspect 1-3Balanced: suspect 7-8Right heavy: suspect 4-6
Weighing 2

If three are suspected, compare one against another. If they balance, the third is heavy. If two are suspected, compare them directly.

Check the reasoning

Each choice reveals why the information strategy works.

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