In play trading ----
Yes you're right what I had meant to give as an example was say back something at 5/1 for £10 potential profit £50, lay in running £20 @ 2/1 potential liability £40 if trade is succesfull win £10 whatever the result. You would think I should know this doing several such trades a day! In my example it should have been exchange odds 6.0 lay odds would be 3.0 to get the DOB.