So you have 3 options when you create a post. You can do 50/50, 100% power up or decline payout.
From what I've seen the 50/50 is more like 75/25 where 75% goes to SBD and the 25% goes to your steem power.
If you are asking about the curation rewards check out this post.
The dollar figure you see at the bottom of your post or comment is not the amount of your payout. You, as the author, are guaranteed at least 75% of the total. As much as 25% goes to the curators (users who upvoted your post). In this instance, you received $7.80 and the curators received $2.20.
thank you so much you have really save me i was checking out the reward split and it didn't make sense and now that you have explained it clearly its much clear that using a bot is profitable with the rewards at 75/25