Sadly, you cannot post the same two works on both platforms. The same goes for all of the shared revenue services and even your own personal websites. Anything that is 100% duplicated will be caught and asked to change or remove (something like that). It also makes Google drop both out of searches completely to a degree.
You can though write on the same niche, topic, and idea as long as you create unique original content for both/all sources! While I never encourage the deleting of an article on another site if it is under-performing and you think you will get better traffic I would move the article to hubpages, if not I would keep the old article on the old site so no backlinks break and the URL is aged.
Hope this helps you out,