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Google·Product Manager·Onsite - Product Sense / Strategy·Intermediate

Intermediate
Jul 2026

Summary

Google PM interview with a classic estimation question about airport metal detector throughput. Pretty standard case format but the specificity of the scenario tripped me up a bit.

Questions Asked (1)

Q1

Pick an airport and estimate how many people pass through the metal detectors in a single day.

Product Analytics & MetricsAdaptability & Ambiguity
Author's notes

I picked a mid-size airport thinking it would be easier to reason about than JFK or LAX, which in hindsight was probably the right call.

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AI HintsAI Generated

Suggested Approach

Choose a well-known airport (e.g., SFO) and break down the daily passenger volume into departing and connecting passengers, then estimate the proportion that passes through metal detectors (security checkpoints). Use round numbers and state assumptions clearly, focusing on logical structure over precise accuracy.

Pro tip: Mention that you're assuming normal operations and that TSA checkpoint throughput varies by time of day; this shows awareness of real-world variability and that you can prioritize key drivers.

1. Select an airport and state assumptions

Pick a major airport you know (e.g., SFO) and state its approximate annual passenger volume. Assume a typical day with no major disruptions.

2. Estimate daily originating passengers

Divide annual passengers by 365 to get daily total. Assume roughly half are originating (start their journey) and half are terminating, so originating passengers ≈ daily total / 2.

3. Account for connecting passengers

Estimate the percentage of passengers who are connecting (e.g., 20-30% at a hub). These passengers also go through security if they arrive from another flight, but many may not re-clear security. Clarify your assumption: typically, connecting passengers do not pass through metal detectors again unless transferring from international or a different terminal.

4. Calculate number passing through metal detectors

Multiply originating passengers by the fraction that go through security (assume 100% of originating passengers). Add any connecting passengers who must re-clear security (e.g., international transfers). This gives total daily metal detector throughput.

5. Sanity-check and refine

Compare your estimate to known TSA throughput rates (e.g., ~200-300 passengers per lane per hour) and number of lanes to see if it's reasonable. Adjust assumptions if needed.

Key Points to Mention

  • Clearly state all assumptions (e.g., annual passenger volume, percentage originating vs. connecting, international transfer rate).
  • Differentiate between originating passengers (who always go through security) and connecting passengers (who usually do not).
  • Use round numbers for easy mental math and to avoid false precision.
  • Consider peak vs. off-peak hours and how that affects metal detector usage, but focus on daily total.
  • Mention that metal detectors are at security checkpoints, not at gates, so only passengers entering the secure area are counted.
  • Acknowledge that airport layout (e.g., separate terminals) might affect whether connecting passengers re-clear security.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.