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.