Market-sizing estimate: number of live apps in a major mobile app store

In a product manager interview at Google, you are asked to estimate how many apps are listed in one of the two major mobile app stores: Apple's App Store or Google Play. Build the estimate from assumptions you can defend, walk through the arithmetic, and check whether the result is reasonable. ```hint Count the builders Rather than guessing a total, ask who actually publishes apps (large organizations, small businesses, professional studios, individual developers) and how many live apps each kind tends to keep in the store. Small, separate assumptions are easier to defend than one big guess. ``` ### Clarifying Questions - Should the estimate be for Google Play, for Apple's App Store, or for both combined, and if combined, does an app listed in both stores count once? - Does "how many apps" mean apps live in the store today, or every app ever published, including those since removed? - Do games count as apps, and does an app offered in many countries or on several device types count as one app? ### What a Strong Answer Covers - Pinning down the store, the live versus ever-published definition and whether games count before estimating. - A clear equation built on a segmentation of publishers or of publishing over time, with each assumption stated as a round number and justified. - Correct, easy-to-follow arithmetic. - A sanity check through an independent method or benchmark, ending in a range rather than false precision. - How the answer would differ between the two stores, and why. ### Follow-up Questions - How would your estimate change if the interviewer meant every app ever published rather than apps live today? - Which single assumption moves your answer the most, and how would you check it with real data at Google? - Why might Apple's and Google's stores hold a similar number of apps even though Android has far more users worldwide?