You can always bet on like 30% odds on a dice site and hope for the best, that's the easiest way. A lot of people above are talking about day trading, but I'd advice very much against that. It's risky, and you can lose a lot very quickly.
Sounds like the best way to loose 7BTC.
If you won more than you lost the gambling sites would go out of buisness. So the system ensures that you loose more than you win.