This is because many games end in a 3 or 7 point difference and the extra half point can either turn a loss into a draw or a draw into a win. Futures Propostion bets usually pay long odds that a specified team will win the playoffs or the season championship. For example before the beginning of the 2000 baseball season a bet that the Baltimore Orioles winning the world series paid 35 to 1 odds. Add all the probabilities form step 1. Call this total t.
Lets look at an example.
The Suncoast casino in Las Vegas offered the following odds to win the Pontiac Excitement 400, which ran on May 5, 2001. For example Ballys, the Paris, and the Flamingo Hilton all offer the same odds, which are all owned by Park Place Entertainment . There is not always an obvious connection among sportbooks. For example the futures at the Rio are much more competitive than at the Las Vegas Harrah's, despite the Rio being owned by Harrah's. The MGM Grand offers the same odds on futures as the Bellagio.