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 1/4 empty again, it is filled with brand Y gasoline. At this time, what percent of the gasoline in the tank is brand Z?	Choose one
A) 21% B) 24% C) 22% D) 20% E) 18.75%
Work with fraction of brand Z in the tank.   1st step: brand Z is 1   2nd step: brand Z is 1/2   3rd step: brand Z is (1/2)*(1/2) + 1/2 = 3/4   4th step: brand Z is (1/4)*(3/4) = 3/16 = 18.75%   Answer (18.75%)
<result>E</result>
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 1/4 empty again, it is filled with brand Y gasoline. At this time, what percent of the gasoline in the tank is brand Z?