I have to calculate odds for a contest. I have 'n' entrants, each with different (but given) number of entry tickets. How do I calculate the odds that any entrant 'x', with his given weighting in the contest, will win the contest? i.e., what's the formula to say "The odds for anyone to win are 1 in blahblahblah"

thanks in advance!

 

The odds will obviously be different for each person, yeah?

All you need is the total number of tickets sold divided by the number of tickets held by the individual.

e.g. If there are 10,000 tickets sold and entrant 'x' has 10 tickets, he (or she ) has a 1 in 1000 chance of winning. If entrant 'y' has 25 tickets, he has a 1 in 400 chance of winning.



I think

 

If you're trying to calculate the probability of winning, or the chance of winning, then tokyo_james is correct.

If you're really trying to calculate "odds", then you need to understand exactly what the term "odds" means; most people use it incorrectly.

Odds means the winnings paid on a given bet. When the odds are fair, they give the proper payoff on the bet so that the expected value of the winnings is zero; the ratio given is the "odds against" winning.

If you own 10 tickets out of 10,000 sold then your likelihood or probability of winning is 10 / 10,000 or 0.001 or 0.1%. The (fair) odds against you winning are 9990:10 = 999:1. Odds (against) are calculated as (number of ways to lose) : (number of ways to win).

William Hill gives the odds against Michael Schumacher winning the Monaco Grand Prix as 4:9. This means that if you bet $9 and Schumi wins you'll win $4--they'll give you back $13. If it were a fair bet (it isn't), then the probability of Schumi winning the race would be 4/13. The actual probability William Hill has calculated is less than 4/13, so they're not paying off as much as they should on a fair bet; that's how they make their money.