214.Eighteen Balls, One Heavy
★★★puzzlesCitadel Securities
You have 18 balls, one of which is slightly heavier than the rest. Using a balance scale that reports which side is heavier or that the sides match, what is the minimum number of weighings guaranteed to find the heavy ball?
Sign in to submit an answer and track it toward your stats.
Sign inHint
Each weighing has three outcomes, so it can cut the candidate pool to about a third. Work out how many rounds of that are needed.
Want timed drills, mental math, and a market-making game too? Try the full practice suite →