Case frameworks
Operations case interviews: capacity, bottlenecks and process
Updated 3 min readBy the MECE Editorial Team
Short answer
Operations cases ask why a process is too slow, too costly or too unreliable, and how to fix it. Map the process step by step, find the bottleneck (the step with the least capacity), measure throughput, cycle time, utilization and quality, then fix the constraint first. Improving any other step will not raise output.
Key takeaways
- Output is set by the bottleneck, the slowest step in the process.
- Little's Law: items in the system = throughput × time in the system.
- Fix the constraint first, then find the next one.
- Separate capacity problems from variability problems.
How do you structure an operations case?
Map the process
List every step from input to output, in order. This split is MECE by construction.
Measure capacity per step
Units per hour each step can handle, and actual demand.
Find the bottleneck
The step with the lowest capacity relative to demand.
Find the root cause
People (staffing, skills), process (layout, handoffs), technology, or supply (materials, variability of arrivals).
Fix and re-check
Add capacity or reduce load at the constraint, then see which step becomes the new bottleneck.
Worked example: why is the lunch line so long?
A fictional Nashville sandwich shop has a long line every lunch. Three steps, with illustrative capacities:
| Step | Capacity (customers an hour) |
|---|---|
| Order at the counter | 60 |
| Make the sandwich (2 staff × 20 an hour) | 40 |
| Pay | 90 |
- Peak demand: 50 customers an hour
- Bottleneck: making, at 40 an hour, so the line grows by 50 − 40 = 10 customers an hour
- Little's Law: with 20 people waiting and 40 served an hour, the wait ≈ 20 ÷ 40 = 0.5 hours, or 30 minutes
- Fix: add a third sandwich maker → 3 × 20 = 60 an hour, above demand
- New bottleneck: ordering and making are both at 60, so the next fix is online pre-ordering
Adding a second cashier would have changed nothing, because payment was never the constraint. That is the central lesson of operations cases.
Which operations metrics should you know?
| Metric | Definition |
|---|---|
| Throughput | Units completed per unit of time |
| Cycle time | Time to complete one unit at a step or in the whole process |
| Utilization | Actual output ÷ capacity |
| First-pass yield | Share of units done right the first time |
| OEE (overall equipment effectiveness) | Availability × performance × quality |
| On-time delivery | Share of orders delivered by the promised date |
| Inventory turns | Cost of goods sold ÷ average inventory |
What questions should you ask in an operations case?
- What is the problem in numbers: late orders, long waits, high cost per unit, defects?
- What are the steps, and what is the capacity and utilization of each?
- Is demand steady or peaky? When does the problem happen?
- Has anything changed: volume, product mix, staffing, equipment?
- What does good look like: a target cycle time, cost or service level?
How do supply chain cases work?
Supply chain cases apply the same logic to a network. The classic SCOR model splits a supply chain into plan, source, make, deliver and return, which is a useful MECE first cut. Typical questions: why are stockouts rising, why is freight cost up, or how many warehouses should we run? Trade-offs are the heart of it: more warehouses mean faster delivery but more inventory and fixed cost.
What are the most common operations case mistakes?
- Improving a step that is not the bottleneck.
- Using averages when variability is the problem. A process can have enough average capacity and still build queues at peaks.
- Skipping quality. Rework consumes capacity at the bottleneck.
- Recommending "hire more people" without sizing it against cost.
Practice this with a live case
Reading builds recognition; solving builds skill. Each case below runs with MECE's AI interviewer, which answers your clarifying questions, pushes back and scores you out of 100.
Operations · E-commerce logistics · medium
An e-commerce warehouse keeps missing same-day cutoffs Practice liveOperations · Healthcare · hard
A Phoenix hospital's emergency department is overcrowded Practice liveOperations · Transportation · medium
A trucking company's empty miles are eating its margin Practice liveOperations · Banking · easy
A bank's call center has long hold times Practice live
Browse all 50 case interview examples and 50 market sizing questions.
Frequently asked questions
What is a bottleneck in operations?
The step in a process with the least capacity relative to demand. It limits the output of the whole process, so improvements elsewhere do not raise throughput.
What is Little's Law?
In a stable system, the average number of items in the system equals the throughput rate times the average time each item spends in it. It links queue length, output and waiting time.
What do operations manager interviews ask?
Expect process and capacity problems, scheduling and staffing questions, quality and cost trade-offs, and behavioral questions about leading teams through change.
Keep learning
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- FoundationsIssue trees: how to break down any business problemRead the guide
MECE (mece.in) is an AI practice platform for case interviews and business problem solving, named after the consulting principle Mutually Exclusive, Collectively Exhaustive. It is not affiliated with McKinsey or any other consulting firm. Companies in worked examples are fictional and their figures are illustrative.
