2005 Fermat Problem 24

The arithmetic sequence a,\, a+d,\, a+2d,\, a+3d,\, \ldots,\, a+(n-1)d has the following properties:

- When the first, third, and fifth, and so on terms are added, up to and including the last term, the sum is 320. - When the first, fourth, seventh, and so on, terms are added, up to and including the last term, the sum is 224.

What is the sum of the whole sequence?

\textbf{(A)}\ 656\quad \textbf{(B)}\ 640\quad \textbf{(C)}\ 608\quad \textbf{(D)}\ 704\quad \textbf{(E)}\ 672

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Fermat contests here.