Interviewer view · keep this screen to yourself
Standard: Should a city switch to electric buses?
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
1. Read the prompt aloud
Read it slowly, then pause. Let the candidate ask questions before they structure.
A large city plans to replace 1,000 diesel buses. An international development bank asks whether electric buses make financial sense. The exhibit compares costs per bus. What do you recommend?
Format note: Difficulty: Standard. Format: interviewer-led, with an exhibit. Industry: Public sector and transport. Region: Global (a large city in a middle-income country). Interview length: about 30 minutes. The company is fictional and all figures are illustrative.
2. Answers to clarifying questions
Give these answers only if the candidate asks. If they ask something not listed, give a sensible answer or say it does not matter here.
If asked: How many buses and over what life?
Answer: 1,000 buses, each used for about 12 years.
If asked: Who pays?
Answer: The city, with a loan from an international development bank for the upfront cost.
If asked: Is power available for charging?
Answer: Yes, at the city's depots, with new charging equipment.
3. The hypothesis a strong candidate states
Listen for an early, testable guess like this one. It does not need to match word for word.
Electric buses cost more to buy but less to run. My hypothesis is that over 12 years they are cheaper in total, and the real problem is financing the higher upfront cost.
4. 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.
- Total cost of ownership over 12 years
- Purchase and charging equipment
- Energy or fuel and maintenance each year
- Key: Total cost per bus and for the fleet
- Upfront financing need
Exhibit 1
Reveal to candidate: when they ask for this data, say "Open Exhibit 1" (they press "Show exhibit 1" on their screen).
| Cost item | Diesel bus | Electric bus |
|---|---|---|
| Purchase price | 250 | 450 |
| Fuel or electricity a year | 50 | 20 |
| Maintenance a year | 20 | 12 |
| Charging equipment (one time) | 0 | 50 |
So-what
Electric buses cost USD 250 thousand more upfront including charging, but save USD 38 thousand a year to run.
5. 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: Diesel bus over 12 years
What a strong candidate does: Purchase plus 12 years of fuel and maintenance (USD thousands).
Diesel total (USD thousands): 250 + 12 × (50 + 20) = 1,090
Step 2: Electric bus over 12 years
What a strong candidate does: Purchase, charging equipment, and 12 years of power and maintenance.
Electric total (USD thousands): 450 + 50 + 12 × (20 + 12) = 884
Step 3: Saving per bus
What a strong candidate does: Diesel total minus electric total.
Saving per bus (USD thousands): (250 + 12 × (50 + 20)) - (450 + 50 + 12 × (20 + 12)) = 206
Step 4: Upfront gap for the fleet
What a strong candidate does: Extra upfront cost per bus (purchase plus charging, minus the diesel price) for 1,000 buses, in USD million.
Extra upfront cost (USD million): 1,000 × ((450 + 50) - 250) ÷ 1,000 = 250
Step 5: Payback of the extra upfront cost
What a strong candidate does: The yearly running saving per bus is the difference in fuel and maintenance.
Payback (years): 250 ÷ ((50 + 20) - (20 + 12)) = 6.58
Step 6: Curveball: battery replacement
What a strong candidate does: Interviewer: "Engineers expect each battery to need replacing once, in year 7, at about USD 100 thousand." The undiscounted saving falls to USD 106 thousand per bus, and payback of the extra spending becomes:
Payback including the battery (years): (250 + 100) ÷ ((50 + 20) - (20 + 12)) = 9.21
Step 7: Discounted at 5 percent
What a strong candidate does: Interviewer: "At 5 percent, USD 1 a year for 12 years is worth about 8.86 today, and USD 1 in year 7 about 0.71." Net present value per bus of switching:
NPV at 5 percent (USD thousands): 38 × 8.86 - 250 - 100 × 0.71 = 15.68
Step 8: Discounted at 8 percent
What a strong candidate does: Interviewer: "At 8 percent, the factors are about 7.54 and 0.58." The year-7 battery now tips the answer negative:
NPV at 8 percent (USD thousands): 38 × 7.54 - 250 - 100 × 0.58 = -21.48
The recommendation to listen for
At the end, say: "The CEO walks in. What is your recommendation?"
I recommend switching to electric buses, but only with low-cost, long-term financing and battery protection. First, before discounting, an electric bus costs about USD 884 thousand over 12 years against USD 1,090 thousand for diesel. Second, one battery replacement cuts the saving to about USD 106 thousand per bus; at a 5 percent development-bank rate switching is worth about USD 16 thousand per bus, but at 8 percent about minus USD 21 thousand. Third, the USD 250 million extra upfront cost therefore needs a long, low-rate loan. Phase the switch depot by depot.
Risks a strong answer names: Electricity prices may rise; Charging depots need reliable grid supply; Staff need training to maintain electric buses.
Next steps: Run a pilot with 50 buses on two routes; Tender with battery warranties and service terms.
Strong versus weak
A strong answer
Compared total cost over the life of the bus, found the upfront gap, and matched financing to the running savings.
A weak answer
Compared purchase prices only and rejected electric buses as too expensive.
Score the candidate
Score each criterion from 1 to 5. A 2 or a 4 sits between the descriptions.
Total
0 out of 25
Score all five criteria to see the band and the feedback template.