It is 3 books for the price of 2.

It is 3 books for the price of 2.
It is 3 books for the price of 2.

It is 3 books for the price of 2.
意思是：三本书仅售两本书的价格.
买两本书的钱就能买到三本

2本书的价格买了三本书

3本书只卖2本的价格。“买二赠一”

花两本书的价钱买了三本书

两元买3本书