Estimation question

Calculate the number of elevators required in a 100-floor building with an occupancy of 100 per floor.

Practice this question out loud. An AI interviewer asks it, follows up like a real interviewer would, and scores your answer. Type or speak.

What this question tests

Whether the candidate can build a queuing-based capacity estimate rather than a naive population-divided-by-elevator-size calculation.

State assumptions: 100 floors, 100 people per floor (10,000 total occupants), and a target of moving everyone comfortably during a peak period like morning rush.
Assume a peak arrival rate, for example 15 percent of building occupants (1,500 people) need to arrive within a 30-minute peak window.
Assume each elevator car holds 15 people and takes roughly 3 minutes for a round trip (load, travel, unload, return) during peak floors.
Calculate single-elevator throughput: 15 people every 3 minutes means 10 trips in 30 minutes, or 150 people moved per elevator in the peak window.
Divide total peak demand by single-elevator throughput: 1,500 divided by 150 gives roughly 10 elevators, then round up for a safety margin, landing around 12 to 14.

Uses peak-period throughput rather than total daily population, since elevators are sized for rush-hour demand, not average load.
States round-trip time and car capacity explicitly as separate, adjustable assumptions.
Adds a safety margin to the raw calculation, acknowledging real-world variability like uneven floor demand.

Dividing total building population by elevator capacity without considering peak concentration or trip time.
Ignoring round-trip time, treating elevator capacity as a one-time rather than repeated throughput.

Chapters of the AI PM course that teach what this question tests.