Estimation question
Imagine there are 10,000 people on Mars. The only way of communication to Earth is through Gmail. How much bandwith is needed?
- Estimation
- Medium
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What this question tests
Tests technical estimation: converting a communication use case into a bandwidth requirement using reasonable assumptions about message volume and size.
How to approach it
- Clarify scope: 10,000 people on Mars communicating with Earth via Gmail, so estimate email volume and size per person per day as the starting point.
- Estimate email volume: assume each person sends and receives a modest number of emails per day given communication delay to Mars, such as a handful of messages daily.
- Estimate average email size: mostly text, but assume some emails include attachments (photos), which dominate total data size compared to plain text.
- Calculate total daily data: multiply population by messages per person by average size per message, separating text-only and attachment-inclusive emails.
- Convert total daily data volume into a required bandwidth (data per second), accounting for the fact that transmission likely happens in scheduled windows, not continuously, given the Mars-Earth communication delay.
- State the final bandwidth estimate as a range with assumptions clearly labeled, rather than one precise number.
What a strong answer includes
- Separates text-only and attachment-heavy emails, since attachments dominate total data volume and would be handled naively if all emails were assumed equal size.
- Accounts for the real-world constraint that Mars-Earth communication happens in transmission windows, not continuously, which changes how volume converts to required bandwidth.
- Builds the estimate through a clear chain, population, messages per person, size per message, transmission window, rather than jumping to a number.
- States the answer as an assumption-driven range, appropriately treating this as a Fermi estimation exercise, not a precise calculation.
Common mistakes
- Ignoring that attachments (photos) would dominate data volume far more than plain text messages.
- Assuming continuous real-time transmission without considering the actual Mars-Earth communication delay and windowing.
Likely follow-up questions
- How would your estimate change if photo and video attachments became the dominant use case instead of text?
- How would you validate this estimate against real interplanetary communication bandwidth figures?
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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