$$100\div \left( 100+400\right) \times 100\textbackslash\% =20\textbackslash\%$$.  ~~ 
A salt solution is made by mixing $100$ g of salt and $400$ g of water. Find the percent concentration of the mixture. 

1: $15\textbackslash\%$ 
2: $20\textbackslash\%$ 
3: $25\textbackslash\%$ 
4: $30\textbackslash\%$ 