"How Many Tennis Balls Fit in a Bus?" – Why Weird Interview Questions Sometimes Make Sense

I have just seen someone on LinkedIn astonished about being asked: "How many tennis balls can fit in a bus?" during a job interview. Many people think these questions don't make sense, but here's why they're actually valuable.

The goal isn't to get the exact right answer – it's to show your thinking process.

For the bus example, you might approach it like this:

• Assume a bus is 6m long, 2.5m high, and 2m wide = 30m³ of volume

• A tennis ball has roughly 4cm in diameter

• For a quick approximation, treat it as a cube: 0.04m × 0.04m × 0.04m = 0.000064m³

• Divide: 30 ÷ 0.000064 ≈ 500,000 balls

This method is known as a Fermi problem – named after physicist Enrico Fermi, who was renowned for making remarkably accurate estimates with minimal data. The key is breaking complex questions into smaller, manageable parts and making reasonable estimates.

Fermi problems teach you to:

• Work with incomplete information

• Make logical assumptions

• Think systematically under pressure

• Accept that "roughly right" is often better than "precisely wrong".

If your initial assumptions are close (bus volume, ball size), your final answer can be surprisingly accurate – often within an order of magnitude of the real answer.

Try it yourself:

• How many pianos are sold per year in the USA?

• How many dentist appointments do people have per month in Spain? How many gas stations are there in your city?

These questions reveal how you think, not what you know – plus how you behave in surprising situations. Whether you're able to ask proper clarifying questions (is the bus empty or full of people? etc.) shows critical thinking skills.