Mǎi yī sònɡ yī

买一送一。

Buy one, get one free.

Notes:

买(mǎi): to buy

一(yī): one

送(sònɡ): to give something free

Example:

A：这个多少钱？

     Zhè ɡe duōshǎo qián?

     How much money is this?

B：100块。现在买一送一。

     100 kuài. Xiànzài mǎi yī sònɡ yī.

     100 yuan. Buy one get one free now.