7/2, 15/1, or 28/3 are ways american bookies list odds
heres how it works
if you have 15/1 odds, you win $15 for every $1 you bet (usually a $5 minimum)
so, for something like 7/2 odds, you would win $7 for every $2 you bet
or for odds such as 2/5, you would only win $2 for every $5 you bet
the closer the fraction is to 0, the closer the bet is seen as being a sure thing, but the smaller your chances of winning much money (its hard to win much when youre only getting $1 for every $13 your betting)
most betting websites such as sportsbook.com or sportsfanatik.com offer info on more indepth bets such as parlays and progressive bets, if youre interested in learning a little more
I get it, you're trying to say that let say in a horse race they would put a 15/2 odd to a horse and you're trying to ask if it is the same with a 7.5/1 odd......
Well basically, it is the same but the horse with a higher denominator number is the mroe favored winner in that particular race.......
Hope this helps.....