The chances of betting on three 4 to 1 chances in a row and having them win, without doing any maths and just going on experience, would have to be about 20% on each or (coincidentally) 1 in 125. I haven't bet on a lot of 125 to 1 horses but I would feel lucky if one won in a couple of hundred bets. I'd say you'd be better betting on the 4 to 1 chances.