Yíbàn yíbàn ba.

一半一半吧。

Fifty-fifty.

Notes:

一半(Yíbàn): half

吧(ba): model particle word which indicates the whole sentence is a suggestion.

Example:

A：这个蛋糕怎么分？

     Zhè ɡe dànɡāo zěnme fēn？

     How do we divide this cake?

B：一半一半吧。

     Yíbàn yíbàn ba.

     Fifty-fifty.