Estimation question
How would you determine how many trips are taken on the London Underground each year?
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What this question tests
Estimation combining ridership per station, service frequency and network scale into an annual total.
How to approach it
- Clarify scope, total annual trips defined as journeys, not individual station taps, on the London Underground.
- Estimate average daily ridership, drawing on the network's known scale as one of the world's busiest metro systems, roughly 3 to 4 million daily trips.
- Account for weekday versus weekend variation, since weekday commuting drives most volume.
- Multiply average daily trips by roughly 365 days, adjusting slightly down for lower weekend and holiday ridership.
- Sanity check the annual total against known comparisons to other major global metro systems of similar size.
What a strong answer includes
- Builds from a daily ridership estimate rather than guessing the annual figure directly.
- Lands on a range around 1 billion to 1.4 billion annual trips and frames it as an estimate, not a fact.
- Adjusts for weekday and weekend variation instead of treating every day as identical.
Common mistakes
- Assuming uniform ridership every day of the year without adjusting for weekends and holidays.
- Confusing individual trips with unique riders, which would understate or overstate the total.
Likely follow-up questions
- How would this estimate change after a major service disruption?
- How would you validate this using Transport for London's public data?
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Learn the skill behind it
Chapters of the AI PM course that teach what this question tests.
- Chapter 2: Data fluency: SQL, logs, and reading the truth yourself
- Chapter 9: Prove it paid off: outcomes, economics, and pricing
- Chapter 14: Get the job: the AI PM interview loop