For example, 3/1 odds mean you profit three times the amount you wagered. AR$1 bet at 3/1 would pay outR$4 in total, or aR$3 profit and yourR$1 original wager. Conversely, 1/3 odds mean you profit a third of what you wagered. AR$30 bet on 1/3 odds would returnR$40 total, or aR$10 profit and yourR$10 original wager.
If a race horse runs 100 races and wins 25 times and loses the other 75 times, the probability of winning is 25/100 = 0.25 or 25%, but the odds of the horse winning are 25/75 = 0.333 or 1 win to 3 loses.