AI & Technical question
How would you design an algorithm to rank ads in the Google Play Store?
- AI & Technical
- Hard
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What this question tests
Tests technical and product thinking on a ranking system with an inherent conflict between relevance and revenue, a classic ads-ranking trade-off.
How to approach it
- Clarify the objective: rank ads in Play Store search/browse results to balance relevance to the user's intent, app quality, and revenue (bid) from advertisers.
- Define the input signals: the advertiser's bid, predicted click-through rate (pCTR) for this user and query, predicted post-click quality (install rate, uninstall rate, app rating), and query relevance.
- Propose the ranking formula structure: rank by expected value, roughly bid times pCTR times a quality multiplier, similar to standard auction-based ad ranking (as used in search ads).
- Address quality control: apps with high uninstall rates or low ratings should get a quality penalty in the multiplier so a high bid cannot buy visibility for a bad app.
- Address user trust: clearly label sponsored results and cap the number of ad slots per results page so organic relevance is not overwhelmed.
- Define success metrics: ad revenue per search, but guarded against user-harm signals like app uninstall rate within a day and search abandonment rate.
What a strong answer includes
- Uses the standard auction-ranking structure (bid times predicted CTR times quality score) rather than inventing an ungrounded formula, showing familiarity with how ad ranking actually works.
- Explicitly ties quality score to post-install behavior (uninstalls, ratings), not just click behavior, which prevents rewarding clickbait-y app listings.
- Names a concrete guardrail metric, next-day uninstall rate, to catch cases where an ad wins ranking but harms the user experience.
- Addresses the user trust dimension (clear sponsored labeling, capped ad density) which interviewers often check for in ads-ranking questions.
Common mistakes
- Designing a pure relevance-ranking algorithm and forgetting this is specifically an ads system with a revenue objective.
- Ignoring quality signals, which would let a high bid dominate rankings for a low-quality or scammy app.
- No mention of user trust or ad density limits.
Likely follow-up questions
- How would you handle a new app with no historical CTR or install data yet?
- How would you detect and penalize apps gaming the quality score?
- How would you A/B test a change to this ranking formula safely?
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Learn the skill behind it
Chapters of the AI PM course that teach what this question tests.
- Chapter 1: Foundations: the model and the decisions it forces on you
- Chapter 8: Evals: define good and make the number defensible
- Chapter 6: Agents and agentic architecture