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How many cups of coffee are sold in a city each day

You run the case. Read the prompt, answer questions from the notes below, and share data only when the candidate asks for it or gets stuck. Score at the end.

Case timer

00:00

Target length:

1. Read the prompt aloud

Read it slowly, then pause. Let the candidate ask questions before they structure.

Estimate the number of cups of coffee sold per day in a city of 2 million people.

Format note: First, define "sold". Most coffee is made and drunk at home, and none of that is sold by the cup. In the United States in 2025, surveys by the National Coffee Association found that about 3 in 10 daily coffee drinkers had coffee made away from home on a given day. So we estimate cups bought ready to drink: from cafes, kiosks, and shops. The survey figure also includes some free coffee at work, so 3 in 10 is an upper bound for cups actually sold.

2. Answers to clarifying questions

This case has no scripted clarifying answers. Answer from the prompt, and say "assume what you think is reasonable" if the prompt does not cover it.

3. A model structure

Compare the candidate's structure with this one. A different split can be just as good if it is clean and fits the problem.

Cups sold per day = adults x share drinking coffee x share buying it outside x cups each
- Adults = population x share who are adults
- Coffee drinkers today = adults x share who drink coffee on a given day
- Buyers today = drinkers x share who buy a cup away from home
- Cups sold = buyers x cups bought each

4. The working, step by step

Each step shows how a strong candidate works it out. Share a new fact from it only when the candidate asks or is stuck, and let them do the math: the result in the dark box is what they should reach.

Step 1: Start from adults, not everyone
What a strong candidate does: Children rarely buy coffee. Assume about 80 percent of the 2 million people are adults.
Adults: 2,000,000 × 0.8 = 1,600,000
Step 2: Coffee drinkers on a given day
What a strong candidate does: Assume about 60 percent of adults drink coffee on a given day. Say this assumption clearly so it can be challenged. It would be lower in a mainly tea-drinking city.
Coffee drinkers today: 1,600,000 × 0.6 = 960,000
Step 3: Those who buy a cup away from home
What a strong candidate does: Assume about 30 percent of today's drinkers buy at least one cup outside the home, close to the 3 in 10 that coffee surveys report.
Buyers today: 960,000 × 0.3 = 288,000
Step 4: Cups each buyer buys
What a strong candidate does: Most buyers buy one cup, some buy two. Assume 1.25 cups each on average.
Cups sold per day: 288,000 × 1.25 = 360,000
Step 5: Cross-check from the supply side
What a strong candidate does: Assume one coffee outlet (cafe, kiosk, or shop selling coffee) for every 2,000 people, and about 350 cups sold per outlet per day. The two methods land close together, which gives confidence.
Cups sold per day, supply side: 2,000,000 ÷ 2,000 × 350 = 350,000

The recommendation to listen for

At the end, say: "The CEO walks in. What is your recommendation?"

My answer is about 350,000 to 360,000 cups a day, because two separate methods land close together. First, from demand: 1.6 million adults, 960,000 coffee drinkers, 288,000 of them buying outside the home at 1.25 cups each gives 360,000. Second, from supply: about 1,000 outlets, one per 2,000 people, selling 350 cups each gives 350,000. The main risk is the assumption that 30 percent of drinkers buy outside the home, which drives the whole estimate. As a next step, test it by counting customers at a few outlets.

Strong versus weak

A strong answer

Defined "sold" before starting, used adults instead of the whole population, said each assumption out loud, and cross-checked from the supply side.

A weak answer

Counted every cup people drink, including coffee made at home, so the answer was several times too high for the question asked.

Score the candidate

Score each criterion from 1 to 5. A 2 or a 4 sits between the descriptions.

This case has no exhibit. Score Exhibit reading on how the candidate used the data you gave them: did they pick out the number that matters and say what it means?

Structuring

1: No clear structure, or a memorized framework that does not fit the problem.
3: A sensible structure, but with some overlap, a gap, or no clear priority.
5: A structure built for this problem, with no overlap and no gaps, a stated hypothesis, and a clear first step.

Math

1: Frequent errors, no units, or needed heavy help to finish.
3: Right answers but slow or messy working, or one error caught late.
5: Accurate and clearly narrated, with units, a sense check, and what the number means.

Exhibit reading

1: Read the chart aloud without finding the number that matters.
3: Found the key number but gave only part of the so-what.
5: Pulled the right number quickly and said what it means for the case.

Synthesis

1: Summarized what was done, with no clear answer.
3: Gave an answer, but with weak reasons or no next step.
5: Answer first, then two or three reasons with numbers, the main risk, and next steps.

Communication

1: Hard to follow: long silences, no signposting.
3: Clear most of the time, with some rambling.
5: Calm and concise, signposted each step, and checked in with the interviewer.

Total

0 out of 25

Score all five criteria to see the band and the feedback template.