Estimation question

How many trains come in and out of Mumbai?

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

Tests structured market sizing skills: breaking an unfamiliar number into segments, applying reasonable rates, and sanity checking the result.

Clarify whether the question means Mumbai suburban locals, long distance trains, or both, since the two differ by orders of magnitude.
Split the suburban network into its three corridors: Western, Central, and Harbour lines.
Estimate a headway (minutes between trains) per corridor during roughly 18 operating hours, such as one train every 3 to 4 minutes on Western line.
Convert headway to trips per line per day, then sum across the three corridors.
Add long distance trains from the major termini (CST, Dadar, LTT, Bandra Terminus, Mumbai Central), assuming a smaller daily count per terminus.
Double the total for in plus out, then sanity check against the fact that Mumbai's suburban system is known to be one of the busiest in the world.

Separates suburban commuter trains from long distance trains rather than lumping them together, since suburban volume dwarfs long distance.
Uses headway as the core lever, e.g. a 3 minute headway over 18 hours implies roughly 360 trips on one line, showing the math rather than a guessed final number.
States every assumption (operating hours, headway, number of termini) explicitly as an assumption, not a fact.
Lands in the thousands per day for suburban trains alone, which is the right order of magnitude.

Treating Mumbai as having one line instead of three separate suburban corridors.
Giving a single number with no visible decomposition or assumptions.

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