Eight balls, one heavier, two weighings
Asked at Optiver, IMC, Akuna
You have eight balls that look identical. Seven weigh the same; one is slightly heavier. Using a two-pan balance,
find the heavy ball in just two weighings.
Show a hint
You don't have to put all eight balls on the scale. What can a "balanced" result tell you about the balls you left off?
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.