If $$a$$@$$b=\frac {a\times b}{a+b}$$ for positive integers $$a$$ and $$b$$ , what is $$5$$@$$10$$? 
Overseas Competition->Knowledge Point->Calculation Modules->Operations with New Definition->Operating Directly->Ordinary Type
Substitute $$a=5$$ and $$b=10$$ into the expression for $$a$$@$$b$$ to get: $$5$$@$$10=\frac {5\times 10}{5+10}=\frac {50}{15}=\frac {10}3$$.  Thus, the answer choice $$\frac {10}3$$ is correct. 