if you divide something fifty-fifty, you divide it equally between two people, companies etc
divide/split/share something fifty-fifty
The companies split the profits fifty-fifty.
We'll share it on a fifty-fifty basis.
go fifty-fifty (on something) (=share the cost of something equally)
We went fifty-fifty on a new TV set.
if there is a fifty-fifty chance of something happening, it is equally likely to happen as not to happen:
a fifty-fifty chance of winning