What the interviewer is checking
Structure
A clear breakdown of the problem into parts that don't overlap and don't miss anything (MECE).
Comfort with numbers
Clean mental math, sensible rounding, and saying what each number means for the decision.
Driving the case
You decide what to look at next and why, instead of waiting to be led.
A recommendation
You end with an answer, the reasons for it, the risks, and what you'd do next.
How to run the case
Restate and clarify
Repeat the goal in your own words and ask about the objective, timeframe and any constraint. Two or three questions, not ten.
Build a structure for this case
Take a moment, then lay out an issue tree. Start from a known shape (profitability, market entry, market sizing) but fit the branches to this company.
Form a hypothesis and test it
Say where you think the answer is and which data would prove or disprove it. Ask for that data.
Do the math out loud
State the approach before calculating, round sensibly, and always say the "so what" of the result.
Synthesize
Lead with the answer: recommendation, two or three reasons, the main risk, next steps.
Common misses
A memorized framework that doesn't fit
Interviewers recognize a generic template. Tailor the branches to the business in front of you.
Math without meaning
A correct number with no implication leaves the interviewer to do the thinking.
No recommendation
"It depends" at the end undoes good work. Pick an answer and give the conditions that would change it.
Worked example
A regional gym chain's profits fell 20% in a year. Why, and what should they do?
- Splits profit into revenue (members × price) and costs (fixed and variable).
- Asks for each over time and finds membership flat but price down after a discount campaign.
- Checks whether the discount brought new members (it didn't, it moved existing ones to the cheaper plan).
- Recommends ending the discount for existing members, keeping it for new sign-ups only, and watching cancellations for a quarter.