My wife says I’m 1/4 horse.

Apparently I’m a horse’s ass.

But it isn't 50/50. It's a whole horse with half a man where his neck and head should be. So it's more like 1 1/4 creatures.

The second one, because if a centaur is already half horse and half human, a half-human half-centaur would be 3/4 human and 1/4 horse.