Week 09 · Days 41–45
Case Studies & Mock Interviews
Practice product sense, estimation, and strategy questions under interview conditions.
Portfolio deliverable · 2 written case study answers + 1 recorded mock interview
Product sense questions
Lesson: Answering 'design a product for X' questions
CIRCLES is a 7-step structure for 'design a product/feature for X' interview questions: Comprehend the situation (clarify the question — what's the goal, what platform?), Identify the customer (who are we designing for — segment, not 'everyone'), Report the customer's needs (what problem are we solving for them?), Cut through with a guiding decision (what's your prioritization principle for this exercise?), List solutions (brainstorm 3-5 ideas), Evaluate tradeoffs (pick 1-2 and justify with pros/cons), Summarize with a recommendation and next steps. The structure matters more than the 'right' answer — interviewers are evaluating your thought process, not whether they'd actually build your idea.
Task: Answer 1 product sense question (written)
Pick a product sense question (e.g. 'Design a feature for Spotify to increase podcast listening') and write a full CIRCLES-structured answer.
Estimation questions
Lesson: Fermi estimation
Fermi estimation breaks a big unknown ('how many people search for flights on Tuesdays?') into smaller, estimable pieces using known anchors (e.g. US population, internet penetration rate, % who travel). The goal isn't accuracy — it's demonstrating structured reasoning under uncertainty. State your assumptions out loud as you go ('I'll assume roughly 300M people in the US, of which maybe 70% are online daily...'), round aggressively (300M not 331M), and sanity-check your final number against something you know (does 'X million DAU' sound plausible for a company of this size?). Interviewers care more about whether your logic is sound and your assumptions are reasonable than whether the final number is 'correct.'
Task: Answer 1 estimation question (written)
Pick an estimation question relevant to your target companies (e.g. 'How many daily active users does [app] have?') and write out your reasoning step by step.
Strategy & 'why' questions
Lesson: Strategy questions ('Why did X do Y?')
'Why did [company] launch X?' questions test whether you can connect a product decision to the business reality behind it. Work through three lenses: Business model (how do they make money — does X create a new revenue stream, defend an existing one, or reduce cost?), Competitive landscape (is X a response to a competitor's move, or an attempt to build a moat before one arrives?), and Growth strategy (does X strengthen an existing growth loop, or open a new acquisition channel?). A strong answer connects at least two of these — e.g. 'I think they launched X primarily to defend retention against [competitor], and it also creates a new upsell path that supports their subscription revenue.' Avoid answers that only describe the feature itself.
Task: Answer 1 strategy question (written)
Pick a recent product launch from one of your target companies and write a short analysis of why you think they made that bet.
Mock interview practice
Task: Record a mock interview (solo)
Record yourself (phone is fine) answering one product sense, one estimation, and one strategy question out loud, timed at 10-15 min total. Watch it back.
Synthesize: Case study portfolio entries
Deliverable: 2 written case studies
Polish your written answers from Days 41-43 into 2 portfolio-ready case study posts, with structure and headers.
Advanced Challenge: Answer an 'AI feature design' interview question
Write a third case study answering a question like 'Design an AI-powered feature for [a consumer marketplace]' using CIRCLES — but go further than most candidates by explicitly addressing: when should the AI act autonomously vs. ask for confirmation (the 'agency' question)? How do you prevent the AI from being confidently wrong in ways that erode trust? What's your 'walk before run' plan for rolling this out? Ground the case study in realistic marketplace behavior and operational constraints.