Market-Sizing Estimate: Rain-Driven Umbrella Purchases in One City

Estimate the number of umbrellas that people in a city buy because of rain. Explain how you break the problem down, state each assumption as you make it, do the arithmetic out loud, and check whether your final number is reasonable. ```hint Ask why anyone buys another umbrella Most adults in a rainy city already own an umbrella. Think about what makes someone buy one anyway, and keep a single unit of time throughout the estimate. ``` ### Clarifying Questions - Which city should I use, and what is its rain pattern: a short, intense rainy season or rain spread through the year? - Is the time window a single rainy day, one rainy season, or a full year? - Do purchases by visitors, businesses and other organizations count, or only purchases by residents? - Do street vendors and online orders count as sales, or only shops? ### What a Strong Answer Covers - Fixing the city, the time window and what counts as a sale before estimating anything. - An equation built from the reasons people buy umbrellas, rather than the population multiplied by a single guessed share. - Round-number assumptions labeled as assumptions, with correct arithmetic and consistent units. - How the answer differs between a single rainy day and a whole season. - A sanity check from an independent angle, and a sense of which assumption moves the answer most. ### Follow-up Questions - How would your model change for a city where rain falls on and off all year instead of in one season? - A store chain wants to know how many extra umbrellas to stock before tomorrow's forecast of heavy rain. How would you adapt your estimate? - Which assumption would you check first with real data, and what data would you use?