Odd Marble Out

What this puzzle interview question tests

This is a medium-difficulty puzzle that quant and trading firms use to assess how a candidate approaches information-theoretic reasoning and systematic problem decomposition. It rewards clear thinking about search strategies and the constraints imposed by a given tool.

The core skill here is recognizing that each weighing outcome carries limited information, and designing a strategy that minimizes the worst-case number of trials needed to isolate a single element from a group. Candidates are expected to think about how many distinct outcomes each weighing can produce, and how to partition the search space optimally at each step.

• Information theory and search efficiency
• Worst-case vs. average-case analysis
• Divide-and-conquer and balanced partitioning
• Adversarial thinking (assuming the worst outcome at each step)