An empty truck weighs $$2000$$ kg. After the truck was loaded, the freight (that is, the load) made up $$80\textbackslash\%$$ of the weight of the loaded truck. At the first stop one fourth of the freight was unloaded. What percent of the loaded truck\textquotesingle s weight did the freight make up after that? ($$2003$$ Math Kangaroo Problem, Level $$7-8$$, Question \#$$17$$) 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Finding the Rate
Actually, we don\textquotesingle t need the weight of the empty truck.  Suppose the weight of the loaded truck before the first stop is $5x$ kg, and the weight of the feight is $4x$ kg. After the first stop, $4x \times \frac14=x$ kg of freight is unloaded. Now, the freight weighs $4x-x=3x$ kg, and the loaded truck weighs $5x-x=4x$ kg. Thus, the percent is $\frac{3x}{4x}=\frac34=75\textbackslash\%$. 