I will expand betting to price further.

If 1.50 / 30.00 = O/L 20
Liability if it wins 20 x .50 (1.50) = -10.00
$20 profit if it falls over for us.

If 20.0 / 30.00 = O/L 1.50
Liability if it wins 1.50 x 19/1 (20.00) = -19.00
$1.50 profit if it falls over for us.


Its the same technique Bookies use to frame their market when laying the field to their book percentage.

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Cheers.