$$\dfrac{100\times50\textbackslash\%+400\times80\textbackslash\%}{100+400}=74\textbackslash\%$$. 
Irene mixes $$100$$ kilograms of dogfood that contains $$50\textbackslash\%$$ rice with $$400$$ kilograms of dogfood that contains $$80\textbackslash\%$$ rice. Find the percent concentration of the rice in the new mixture. 
Options:
(A) $$70\textbackslash\%$$ 
(B) $$72\textbackslash\%$$ 
(C) $$75\textbackslash\%$$ 
(D) $$74\textbackslash\%$$ 