A car uses 20 gallons of gas to travel 400 miles. Mr. Montero's car has 8 gallons in it. How many more gallons of gas does he need to travel 600 miles, back and forth? Let's think first. Chain of thought:
Mr. Montero is traveling a total distance of 600 miles + 600 miles = 1200 miles. There are 1200 miles / 400 miles = 3 sets of 400 miles in 1200 miles. So Mr. Montero needs 20 gallons / set x 3 sets = 60 gallons in all. Since his car has 8 gallons already, then he needs to add 60 gallons - 8 gallons = 52 gallons more.
Therefore, the answer is 52.