The Boston Globe has a great story on MIT students using hard sums to extract an “almost guaranteed” 15-20% return from the Massachusetts State Lottery's Cash WinFall game. Even better, lottery officials knew what was going on and did nothing to stop it – in some cases actively encouraging the syndicates – because it boosted their own bottom line.
The Irish were pioneering this sort of thing back in 1992. A 28-member syndicate headquartered in Scruffy Murphy's worked out that they could make a guaranteed profit by buying up all possible combinations with a pre-marked stash of a quarter of a million ticket slips. The National Lottery figured out what they were up to and did their best to stop them, but the syndicate still came out of it with about £310,000 before expenses. It looks like Stefan Klincewicz (the author of the scheme) is still dining out on the story, if his LinkedIn page is any guide.