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Peloton·Software Engineer·Onsite - Multi Round·Intermediate

Intermediate
Apr 2026

Summary

Interviewed at Peloton and got hit with a classic fermi estimation question. Not much else to report.

Questions Asked (1)

Q1

How many ping pong balls can fit inside a Boeing 747?

Adaptability & AmbiguityProduct Analytics & Metrics
Author's notes

Classic fermi estimation.

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AI HintsAI Generated

Suggested Approach

Break the problem into manageable parts: estimate the volume of a Boeing 747's interior and the volume of a ping pong ball, then divide to get a rough count. State your assumptions clearly and focus on the reasoning process rather than the exact number.

Pro tip: Acknowledge that this is a Fermi problem and that the exact answer is less important than your structured approach; mention that you'd validate assumptions with real data if available.

1. Clarify assumptions

Ask clarifying questions to define the scope, such as whether the plane is empty or has seats, and whether 'fit' means packed tightly or loosely.

2. Estimate the volume of the 747

Approximate the interior volume by modeling the fuselage as a cylinder and adding the volume of the wings and cargo areas if relevant.

3. Estimate the volume of a ping pong ball

Calculate the volume of a ping pong ball using the formula for a sphere (4/3 π r³) with a typical radius of 2 cm.

4. Account for packing efficiency

Apply a packing factor (e.g., 0.64 for random close packing of spheres) to account for the empty space between balls.

5. Compute and sanity-check

Divide the adjusted plane volume by the ball volume to get the number, then sanity-check by comparing to known benchmarks or simplifying the model.

Key Points to Mention

  • Use of Fermi estimation to simplify complex problems
  • Clear statement of assumptions (e.g., empty plane, spherical balls, packing factor)
  • Volume calculation for a cylinder (fuselage) and sphere (ball)
  • Packing efficiency and its impact on the final count
  • Sanity-checking the result against known data or common sense
  • Emphasis on the problem-solving process over the exact numerical answer

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.