A Google Interview Question

I recently interviewed with Google for a product manager position. I wasn’t really looking since I have been actively working on my startup. But since the Google recruiter found me on LinkedIn and reached out to me, I went ahead and gave the whole interview process a shot. Overall, the process was professional and well organized. I thought I answered most of the questions well except for this one:

For any given day, calculate the total number of miles traveled by all the passengers using the subway.

Just want to share this!

select sum(distance_between_subway_stops(entered,exited) from subway_info where date=any_given_day;

Here is how I would have approached. The average commute time is 40 mins for New Yorker. The population is 12 millions and during a work day it goes up to 20 million.

So I assumer 20 Ml . Out of the 40 mins assume 20 mins spend on 15 mins- 20 mins spend on path, LIRR, NJ Transit etc.. so this gives around 20 - 25 mins of average commute in subway.

Assuming arounds 40 percentage uses subway

8 million * 5 - 7 miles= 40 - 50 million miles..