An empty fuel tank is filled with brand Z gasoline. When the tank is 1/4 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?  Choose the correct choice from the following options:  A) 31.25 %  B) 30 %  C) 40 %  D) 50 %  E) 45 %

Rationale: work with fraction of brand z in the tank . 1 st step : brand z is 1 2 nd step : brand z is 1 / 4 3 rd step : brand z is ( 1 / 2 ) * ( 1 / 4 ) + 1 / 2 = 5 / 8 4 th step : brand z is ( 1 / 2 ) * ( 5 / 8 ) = 5 / 16 answer ( a )
Answer: A