@nunarita for each unit of money you bet, you get 10 if you win. The others are 1:1, so for each unit of money you bet you get the same amount if you win. The odds are 50% chances that either wei hao, huang que or wang ruoling come first. Qin Nan's is 10:1, so 9% chances of winning.
If for example you bet on wei hao and win, you get your initial bet back plus the winnings, so you effectively double your money.
Note that the odds don't necessarily have to add up to 100%.
If you lose, you lose your bet and win nothing extra. So basically the people here are voting on their favorites since the odds are all the same. Betting on Qin Nan is too risky, as there's a 91% chances you lose everything, but there's a big payout if he does win. Unfortunately, the audience doesn't know Qin Nan's the protagonist and that there's actually a 100% chance that he places first