Estimate total pollution created by vehicles passing through a busy roundabout in a day.

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Recent activity on Jan 24, 2019
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Harsh asked on Jan 23, 2019

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updated an answer on Jan 23, 2019
McKinsey Senior EM & BCG Consultant | Interviewer at McK & BCG for 7 years | Coached 350+ candidates secure MBB offers

Pragmatic approach:

1. Segment into types of vehicles

2. Estimate pollution intensity per vehicle type (e.g., if it takes 30 seconds to pass the roundabout on average, what is the pollution per 30 secons?)

3. Estimate number of vehicels for each type per time of the day (rush hours vs non-rush hours)

4. Multiply sum of 3. with 2. for each type and sum up

Cheers, Sidi


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replied on Jan 24, 2019
Ex-Bain + MBA recruiter + experienced hire

Another approach:

1. Clarify what constitutes "passing through" and "busy". Let's define "passing through" as cars on the circle itself (not cars waiting to enter the circle). Let's define "busy" as a roundabout that constantly has cars on it. Defined thus, it doesn't matter whether it's rush hour or not, since the density of traffic won't change.

2. Clarify the time-frame -- reasonably, a day = 9am - 9pm.

3. Clarify a) the length of the roundabout circle to determine how many cars can drive on it at once; b) the average length of a car; c) the average distance between cars driving on it -- then you can determine the number of cars driving on the roundabout

4. Make a reasonable assumption about average car emissions (segmenting more / less depending on the theoretical precision you want or think the interviewer wants)...and note your units in terms of emissions/distance or emissions/time (emissions/hr would be consistent with #2, our timeframe)

5. Answer should be #2 * #3 * #4

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replied on Jan 23, 2019
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School


Would be good if you come up with your ideas first.

Think about calculating the number of different types of the cars in the streets (Hint - it's always easier to start with non-commercial segment)


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Sidi gave the best answer


McKinsey Senior EM & BCG Consultant | Interviewer at McK & BCG for 7 years | Coached 350+ candidates secure MBB offers
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