I blanked for a second and just started talking through what I remembered from school.
Break the problem into smaller, estimable components using known reference points (e.g., distance between two cities at the same longitude) and simple geometry. State your assumptions clearly, perform the calculation step-by-step, and sanity-check the result against known facts. Emphasize the process over the exact number, as interviewers care more about structured thinking.
Pro tip: After arriving at an estimate, briefly mention how you would validate it with a quick search or by cross-referencing with known data (e.g., Earth's diameter is about 12,742 km). This shows you value accuracy and know when to leverage available resources.
Confirm what is being asked: the circumference at the Equator, not a meridian. Restate the problem to ensure alignment and mention that you'll use estimation techniques.
Select a familiar reference point or method. For example, use the distance between two known cities on the Equator (e.g., Quito to Singapore is not on Equator; better: Quito to Macapá) or recall that the meter was originally defined as 1/10,000,000 of the distance from Equator to North Pole, leading to a quarter circumference of ~10,000 km.
If using the meter definition: quarter circumference = 10,000 km, so full circumference = 40,000 km. If using city distances: estimate the distance and multiply by the fraction of the circumference. Show your math clearly.
Verify the estimate against known facts: Earth's diameter is about 12,742 km, so circumference = π * diameter ≈ 40,030 km. Adjust if necessary and state the final estimate with appropriate precision.
Summarize your approach, the assumptions made, and the final estimate. Reflect on potential sources of error and how you might improve the estimate with additional data.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.