富与贵 Fù yŭ guì Rich and Expensive

老师: 三中全会后，中国最大的变化是什么？
Lăoshī: Sānzhōngquánhuì hòu, zhōngguó zuì dà de biànhuà Shì shénme?
Teacher: What was the greatest change in China after the Third Plenary
Session?
学生: 三中全会后，中国最大的变化是农民越来越贵了。
Xuésheng: Sānzhōngquánhuì hòu, zhōngguó zuì dà de biànhuà Shì nóngmín yuè lái yuè guì le.
Student: The greatest change was that the farmers became more and more expensive after the Third Plenary Session.
老师: 是富不是贵。
Lăoshī : Shì fù bú shì guì.
Teacher: It is rich, not expensive.

Analysis
In this joke, the student can't distinguish between the two words 富(fù) and 贵(guì). They both mean prosperity. 富(fù) means rich and wealthy, so people usually use it to refer to someone who is very successful, while 贵(guì) means expensive, so people usually use it to describe something expensive to buy.