Interviewer view · keep this screen to yourself

A parts factory in Vietnam moves from big batches to flow

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.

A factory in Bac Ninh, Vietnam makes 2,000 electronic parts a day. Because each step makes big batches, about 40,000 half-finished parts sit between steps at any time, each worth USD 5 of materials and work. By making small batches and passing them straight on, it can cut this to 10,000. Use a carrying cost of 22 percent a year. What does flow gain? (Fictional factory, illustrative figures.)

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.

Gains from flow: lead time, cash freed, yearly carrying cost
- Lead time = parts in the system / parts finished a day (Little's Law)
- Key: Cash freed = parts removed x value per part
- Yearly saving = cash freed x carrying cost

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: Lead time before
What a strong candidate does: 40,000 parts in the system, 2,000 finished a day.
Lead time before (days): 40,000 ÷ 2,000 = 20
Step 2: Lead time after
What a strong candidate does: 10,000 parts in the system, still 2,000 a day.
Lead time after (days): 10,000 ÷ 2,000 = 5
Step 3: Cash freed
What a strong candidate does: 30,000 fewer parts at USD 5 each, released once.
Cash freed (USD): (40,000 - 10,000) × 5 = 150,000
Step 4: Yearly saving
What a strong candidate does: 22 percent of the stock no longer held.
Carrying cost saved a year (USD): 150,000 × 0.22 = 33,000

The recommendation to listen for

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

Moving to flow cuts the time a part spends in the factory from 20 days to 5, frees USD 150,000 of cash once, and saves about USD 33,000 a year in carrying cost. The bigger gains are often hidden: with 5 days in the system, a fault at the first step is found in days, not weeks, so far fewer parts are made wrong, and the factory can promise customers shorter delivery times. The risk is a breakdown: with little stock between steps, one stopped machine stops the line, so keep a small buffer in front of the bottleneck.

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.