A salt solution is made by mixing $100$ g of salt and $400$ g of water. Find the percent concentration of the mixture. 
Overseas Competition->Knowledge Point->Word Problem Modules->Word Problems in Economics->Basic Profit and Loss Concepts->Calculating Price from Cost and Profit
$$100\div \left( 100+400\right) \times 100\textbackslash\% =20\textbackslash\%$$.  ~~ 