A mixture of $$30$$ litres of paint is $$25\textbackslash\%$$ red tint, $$30\textbackslash\%$$ yellow tint and $$45\textbackslash\%$$ water. Five litres of yellow tint are added to the original mixture. What is the percentage of yellow tint in the new mixture? 
Overseas Competition->Knowledge Point->Word Problem Modules->Concentration Problems->Basic Concentration Problems
Since $$30\textbackslash\%$$ of the original $$30$$ liters of paint was yellow, and $$5$$ liters of yellow paint were added to make the new mixture, there are $$9+5=14$$ liters of yellow tint in the new mixture. Since only $$5$$ liters of paint were added to the original $$30$$, there are a total of $$35$$ liters of paint in the new mixture. This gives $$40\textbackslash\%$$ of yellow tint in the new mixture, which is $$40$$. 