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. 
If $$a$$@$$b=\frac {a\times b}{a+b}$$ for positive integers $$a$$ and $$b$$ , what is $$5$$@$$10$$? 

a. $$\frac 3{10}$$ 
b. $$1$$ 
c. $$2$$ 
d. $$\frac {10}3$$ 
e. $$50$$ 