Estimation: total email volume arriving in San Francisco inboxes

In a product manager interview at Google, you are asked to estimate the number of emails the city of San Francisco receives. Decide exactly what you are counting, build an equation, state the assumption behind each input, work through the arithmetic and check whether the result is believable. ```hint Split by who receives the mail People's email volumes differ enormously: an office worker's work inbox alone can outweigh a retiree's entire day of mail. Divide the population into a few groups with very different email habits and estimate each group separately. ``` ### Clarifying Questions - Does "the city of San Francisco" mean the people in the city, or the city government (the City and County of San Francisco) as an organization receiving email? - Over what period should the estimate run: a day, a week or a year? - Does spam that the provider blocks before delivery count, or only mail that reaches an inbox or folder? - Should the count cover only residents, or also the many people who commute into the city and receive work email there? ### What a Strong Answer Covers - A precise definition of what is counted (whose mail, which period, whether spam counts), agreed before calculating. - A clear equation that segments the population by email behavior, such as office workers, other workers, non-working teens and adults, and young children. - Explicit, labeled round-number assumptions and arithmetic that is easy to follow and correct. - A sanity check against an independent reference point, and a note on which input the result is most sensitive to. ### Follow-up Questions - How would the estimate change if work email received by commuters counted toward San Francisco? - Which single input moves your answer the most, and how would you get a better value for it? - If you were estimating email received by the city government instead, how would you change the approach?