AutoGas problem

This one would make a good interview question at Microsoft:
How many auto gas stations are needed in Bangalore?

Most of the auto-rickshaws in Bangalore are run on gas (LPG/CNG). With the boom in population, and need for transportation, the auto-rickshaw population has exploded (currently ~2,50,000). Unfortunately, the autoGas filling stations have not. There are only a handful (~20) of those stations in the city. Due to this acute shortage, one sees autos lining up (see pic above) for upto 1.5 hrs just to fill gas!

So, here is the question in more detail:

Assuming that there are 2,50,000 autos in Bangalore, and

the gas mileage of an auto is about 20 Km/litre, and

the tank capacity is 12 litres, and

an average auto driver does about 50 Km/day,

how many autoGas filling stations are needed in order to reduce the wait time for filling to zero?

Phew, that was a mouthful.

Let me know when you find the answer, and in the meanwhile, I will be working on it too.