A $$12$$ $$\text{mg}$$ metal containing $$40 \%$$ nickel was combined with a $$13$$ $$\text{mg}$$ metal containing $$60 \%$$ nickel. Find the percent concentration of nickel in the new metal. 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Finding the Rate