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Estimationstretch

Estimate how many people are on flights over the US right now.

How to approach it

Start with flights in the air at a given moment, then multiply by average passengers per flight.

How a strong answer opens

“I'll estimate how many flights are in the air at one moment, from daily flights and average flight length, then multiply by passengers per flight.”

Outline of a strong answer

Try answering out loud for a few minutes before you open this.

  1. Clarify: commercial passenger flights, a typical weekday afternoon
  2. Estimate daily US flights
  3. Average flight length in hours and hours of active flying per day
  4. Flights in the air at once = daily flights x hours each / active hours
  5. Average passengers per flight
  6. Multiply, then sanity-check against a big airport's daily passenger count

Where this question usually goes wrong

Multiplying daily flights by passengers and calling that the number in the air right now, forgetting most flights are on the ground at any given moment.

Learn the method

Top-down and bottom-up in Module 3, Estimation.

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