Estimation question

How much will it cost for Facebook to add one additional user?

Practice this question out loud. An AI interviewer asks it, follows up like a real interviewer would, and scores your answer. Type or speak.

What this question tests

Cost estimation: breaking down infrastructure and support costs per incremental user for a large scale social platform.

Clarify scope: marginal cost of serving one more active user, not the average cost including fixed overhead like R&D.
List the main variable cost buckets: data storage, compute for feed ranking, content delivery, and customer support.
Estimate each bucket per user per year, for example a few dollars for storage and compute combined.
Add a small allocation for support and moderation costs per user.
Sum the buckets to reach a per user marginal cost, then sanity check against Facebook's known revenue per user for plausibility.

Separates fixed costs like R&D and office overhead from true marginal costs like storage and compute, since only the latter apply to one new user.
Lands on a small dollar figure, for example a few dollars per year, and explains this is far below average revenue per user.
Sanity checks the number against Facebook's reported ARPU to show the business model works with large margin.

Including fixed costs like headcount or R&D in a marginal cost estimate, which inflates the number unrealistically.
Skipping the sanity check against known revenue per user.

How would this marginal cost differ in a market with expensive data infrastructure?
How would video content change this estimate?