I'm also going to try my hand at estimating the number of gas stations in the country:

270 million people in the country. 1 car per 3 people, makes about 90m cars. Each filled up about twice a week, makes 180m fillups per week. Each station on average does about 12 fillups per hour for about 12 hours a day. So in a week each station does about 1000 fillups per week. Thus there should be about 180,000 gas stations in the country. This comes out to about 1500 people per gas station. Thus my home town would need about 40,000/1,500 = 28 gas stations serving my home town. This seems a tad on the high end, but still reasonable.

David (Speyer) mentioned the following microsoft interview question a friend mentioned to him. There is a mouse in the middle of a circular lake. There is a cat on the shore. If the mouse reaches the shore and the cat isn't waiting then he escapes safely into the high grass. How fast does the mouse need to be able to swim relative to the walking speed of the cat to be able to reach the shore safely?