Tuesday, June 17, 2014

How many gas stations are there in the city of Paris?


# of inhabitants in Paris: 10 m
# of cars: 2 m (Assumption: for every 5 people)
# of commercial vehicles: 0.5 m (Assumption: 4 times less than cars)

Assumption: Cars have tanks of 50 liters and replenish them every 10 days.

Fuel consumption for a car: 5 liters/day
Fuel consumption for a commercial vehicle: 25 liters/day (Assumption: 5 times more than of cars) 
Weighted average of fuel consumption: 20% * 25 + 80% * 5 = 9 liters/day

Daily city demand: 9 liters/day * 2.5 m = 22.5 m liters 

# pumps per station: 10 (Assumption)
Time a vehicle spends at a pump: 15 minutes
# of vehicles a pump can serve in an hour: 60 / 15 = 4
Stations are open for: 10 hours (Assumption)
# of vehicles a gas station can serve per day: 10 * 10 * 4 = 400

Liters bought per visit (cars): 50 liters (Assumption)
Liters bought per visit (commercial vehicles): 100 liters (Assumption)
Weighted average of liters bought per visit: 20% * 100 + 80% * 50 = 60 liters
Capacity of a gas station: 60 liters * 400 = 24'000 liters

# of gas stations: 22.5 m / 24'000 = 937.5

Saturday, June 14, 2014

Fastest to a Billion

This chart shows the number of years it took billionaires to attain a $1 billion net worth (liquid or illiquid assets) after having founded their enterprise.


Source: Forbes