Need Help, Greyhound Bet Type

[puscus]

My usual bet for the greyhounds involve selections for every race at a meeting. For example I might have Romford First 8 Races 5 x 6 28 1p R/F Doubles Total = £1.12 I don't usually bet that much on the dogs but this type of bet as proved successful for me. Now today I was talking to a guy in the bookies and he was telling me about doing a Combination Forecast instead because I have more chance of winning more. Now from what I understand is that a Combination Forecast involves picking 3 dogs and two of them have to finish 1st and 2nd. Can this be done on the types of bets I do and how much more would it cost to have them reversed.

[BillyHills]