Can someone help me on this problem? I need to know how to calculate the probability of winning a 2 horse parlay, compared to betting one horse to win. Let's say I have created an accurate/correct odds line for two races being run 5 minutes apart. I know you should only bet overlays, but to keep it simple let's say that the only horses I'm interested in for these two races are going off at exactly the same odds as my line says they should be. Should I just bet the one 8-1 shot, or would I be better off betting a parlay on two 2-1 shots in the two races? The payoff is the same, $18. I come up with the probability of the 8-1 shot winning as 11.1%, and the two horse parlay as 10.9%, so I would bet the 8-1 shot. Is this correct? Thanks.