Asifpirlo wrote:

An empty fuel tank is filled with brand Z gasoline. When the tank is half empty, it is filled with brand Y gasoline. When the tank is half empty again, it is filled with brand Z gasoline. When the tank is half empty again, it is filled with brand Y gasoline. At this time, what percent of the gasoline in the tank is brand Z?

A. 50%

B. 40%

C. 37.5%

D. 331⁄3%

E. 25%

Let’s say the tank starts with 32 gallons of gas (we use the number 32 because we can take half of this number many times over and it still will be a whole number).

To start, there are 32 gallons of Z.

When the tank is half empty and filled with brand Y, that gives us:

16 gallons of brand Z and 16 gallons of brand Y.

When the tank is half empty again and filled with brand Z, that gives us:

8 gallons of Brand Y and 8 + 16 = 24 gallons of brand Z.

When the tank is half empty again and filled with brand Y, that gives us:

4 + 16 = 20 gallons of brand Y and 12 gallons of brand Z.

Thus, 12/32 = 3/8 = 37.5% of the tank is filled with brand Z.

Answer: C

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Jeffery Miller

Head of GMAT Instruction

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