Prove that if $\displaystyle r_{1}, r_{2},..., r_{\Phi (m)} $ is a reduced residue system modulom, andmis odd, then $\displaystyle r_{1} + r_{2} + ... + r_{\phi (m)} \equiv 0. $ (modm).

and

What is the remainder when $\displaystyle 473^{38}$ is divided by 5?

Any help would be appreciated! Thanks!