$n\_1=\frac{20}{20+30}\times100\textbackslash\%=40\textbackslash\%$;  $n\_2=\frac{20}{20+30+50}\times100\textbackslash\%=20\textbackslash\%$. 
Jack mixed $20$ grams of sugar with $30$ grams of water. What is the percent concentration of the sugar solution? Then Jack added $50$ grams of water. What is the percent concentration the sugar solution? 
a: $$40 \textbackslash\% $$; $$20\textbackslash\% $$. 
b: $$40 \textbackslash\% $$; $$25 \textbackslash\% $$. 
c: $$50 \textbackslash\% $$; $$20 \textbackslash\% $$. 
d: $$50 \textbackslash\% $$;~$$25 \textbackslash\% $$. 