Case Type: estimate/guesstimate.
Consulting Firm: Oliver Wyman first round job interview.
Industry Coverage: Oil, Gas, Petroleum Industry; Automotive, Motor Vehicles.
Case Interview Question #00303: How many gallons of gasoline does an average gas station in the United States sell on an average day?
Possible Solution:
Answering this estimation/guesstimate type of case questions requires answering a number of sub-questions (SQ) first. To estimate the number of gallons of gasoline sold by an average gas 
station in a day, the following sub-questions and possible solutions could be used:
1. What is the average number of sales per gas station per day?
2. What is the average volume of one sale (average tank size)?
3. Calculate the number of gallons of gasoline sold per day by multiplying 1 and 2.
Possible Answers:
1. Let’s say a regular gas station is the U.S. has 8 gas pumps on average.
Assume that in early morning (from 6am to 8am) and late evening (8pm to 12am), when there are less cars on the road, sales frequency is about every 20 minutes, thus 6 hours * 3 sales per hour = 18 sales per gas pump.
During normal business hour (from 8am to 8pm), sales frequency is about every 10 minutes. Thus,
