A Windows default change lifted usage — did it cause durable growth?
Measure impactHardProblem. A Windows update made Bing the default search in a set of markets, and query volume rose there ~18%. Leadership credits the change with the full lift and wants to invest more. You can't randomize the default per user. Did it cause durable growth, and how would you estimate the true effect?
Before you reveal: say your answer out loud, as if you were in the real interview — get your reasoning across clearly first. There is no single correct answer: reading what the interviewer is really after and defending your own thinking is what makes an answer strong.