Either .643 or .875. The only given info you have is 50% chance of winning, and 50% chance of losing or getting 2nd, 3rd, 4th, 5th, 6th, 7th, or 8th place. If getting 2nd is just as easy as getting 8th (unlikely) then that 50% gets divided evenly for a 7.14% chance of getting one of those finishes. That is how I get .643. Another way to look at is 50% shot of getting 1st place. To get second is then a 25% chance, and 3rd is 12.5% chance...