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EstimationFoundationalFree
Market Sizing / Estimation
Tests structured estimation and explicit assumptions - the number matters less than the reasoning.
Interview prompt
How many [items, e.g. ride-share trips happen in New York City] per day?
What interviewers evaluate
- Do you state assumptions explicitly and reason top-down or bottom-up?
- Do you decompose the problem into estimable pieces?
- Are your intermediate numbers reasonable and sanity-checked?
- Do you arrive at an answer and discuss what would change it?
A framework to structure your answer
- Clarify - define the item and scope (geography, timeframe, what counts).
- Pick an approach - top-down (start from a big population and narrow) or bottom-up (build from units of activity).
- Decompose - break into factors you can estimate (population × adoption × frequency).
- Estimate each factor - state each assumption out loud with a round, defensible number.
- Compute & sanity-check - multiply, then sense-check against something you know.
Strong sample answer
Try structuring your own answer first, then reveal a strong worked example.
Common variants
- How much storage does YouTube need per day?
- How many pizzas are sold in the US per year?
- Estimate the number of queries Google handles per second.
Pitfalls to avoid
- Not stating assumptions, so the reasoning can't be followed or corrected.
- Reaching for a precise-looking number with no decomposition.
- Using wildly off base numbers and not sanity-checking.
- Getting lost in arithmetic instead of structure (round aggressively).
- Forgetting to give a final answer and a range.
Likely follow-ups
- Which assumption is your answer most sensitive to?
- How would the number change for a weekend?
- How would you validate this with real data?