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A mixture of $25$ liters of paint is $16 \textbackslash\%$ red tint, $24\textbackslash\%$ yellow tint and $60\textbackslash\%$ water. $15$ liters of yellow tint are added to the original mixture. What is the percent of yellow tint in the new mixture? (adapted from 2007 AMC 8, Question \#17 ) 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Percentages Word Problems
The original mixture contains $25\times 24\textbackslash\% = 6$ liters of yellow tint.  $$15$$ liters of yellow tint is added to the mixture, the new mixture now has $6+15=21$ liters of yellow tint.  New percent of yellow =$\frac{21}{25+15} =52.5\textbackslash\% $ 