I froze for a second because I genuinely wasn't sure if they wanted me to actually know this or just structure my way through it.
Break the problem into manageable components: first estimate the total length of the German autobahn, then determine the average number of lane divider stripes per kilometer based on lane count and stripe spacing. Use reasonable assumptions and round numbers to simplify calculations, and clearly state your assumptions so the interviewer can follow your logic.
Pro tip: Focus on demonstrating structured thinking and the ability to make defensible assumptions rather than getting the exact number; interviewers care more about your approach than the final figure. Acknowledge that this is a Fermi problem and that your answer will be an order-of-magnitude estimate.
Ask clarifying questions to define what counts as a lane divider stripe (e.g., dashed lines between lanes, solid lines on edges) and whether to include all autobahn lanes or just specific ones. Confirm that the goal is an estimate, not an exact count.
Recall or estimate the total length of the German autobahn network (approximately 13,000 km). If unsure, use a rough figure and state it as an assumption.
Assume an average number of lanes per direction (e.g., 2 lanes per direction, so 4 lanes total) and note that some sections have more or fewer. This gives the number of lane divider lines per kilometer.
For each divider line, estimate the stripe length and gap (e.g., 6 meters stripe, 12 meters gap, so one stripe every 18 meters). Then compute stripes per kilometer per divider line (1000 / 18 ≈ 55.6).
Multiply total length by number of divider lines by stripes per kilometer to get total stripes. Round to a sensible order of magnitude and sanity-check against intuition (e.g., millions of stripes).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.