Dawgball, there may be a quicker way, but I use the following formulas (in Excel) to work out the size of the scalp and the relative wager sizes:
(1) Convert the moneyline odds in decimal format
For favorites, use the expression 1-(100/odds)
So -225 is 1-(100/-225) = 1.44
For dogs, use the expression (100+odds)/100
So +300 is (100+300)/100 = 4.00
(2) Calculate the relative wager sizes:
For both, use the expression odds/(odds + other odds)
So for example above, for the favorite:
Relative wager size is 4.00/(1.44+4.00) = 72.5%
For the dog:
Relative wager size is 1.44/(1.44+4.00) = 26.5%
(3) Use either to calculate the size of the scalp:
Favorite wager size * favorite odds:
73.5% * 1.44 = 1.06
Dog wager size * dog odds:
26.5% * 4.00 = 1.06
Hence there is a 6% scalp on the -225/+300 lines. I wager $735 on the favorite and $265 on the dog to make a guaranteed profit of $60.
Hope this helps. Like I said, easiest if just written as a 4*2 table in Excel.
