Fractional odds show profit first, then stake. Odds of 5/2 mean 5 units of profit for every 2 staked. To get decimal odds, divide the top number by the bottom and add 1. To get the implied probability, divide the bottom number by the sum of both numbers. Odds of 1/1 are even money, and odds shorter than that, such as 1/2, mean the selection is the favorite.
Example
At 5/2, a 2 unit stake wins 5 in profit and returns 7. That equals decimal 3.50 and an implied probability of 2 divided by 7, about 28.6%.