I know some people win more than others, but I do not believe it would be possible to win 1 out of 10 contests you enter. Found this article, and this woman estimates she wins 10% of the time and enters 1 to 2 hours a day. That would add up to hundreds of prizes a month! I know that this was probably just added to up the article some, but it is setting unrealistic expectations.
Article link:
http://www.fergusfallsjournal.com/2012/05/10/sweeping-up-the-winnings/
Article link:
http://www.fergusfallsjournal.com/2012/05/10/sweeping-up-the-winnings/