Answer
a)999:1
b)499:1
c)Wrong description.
Work Step by Step
a) We know that $odds=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes-number \ of \ good \ outcomes}$, hence $odds=\frac{999}{1000-999}=\frac{999}{1}$, hence the odds are 999:1.
b)We know that $odds=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes-number \ of \ good \ outcomes}$, hence $odds=\frac{499}{500-499}=\frac{499}{1}$, hence the odds are 499:1.
c) The odds against winning are 999:1, hence the odds for winning are 1:999, not 1:1000, hence the description is wrong.
