Datong in Shanxi is expensive, but Xining in Qinghai is not. The price of sheep hind legs varies from place to place. For example, in RT Mart supermarket in Datong, the price of sheep's hind legs is one catty in 26 yuan, and that of 40 yuan is higher than that of 26 yuan. Therefore, 40 yuan a catty of sheep hind legs is expensive in Datong.

The price of sheep hind legs in Beijing Hualian Supermarket in Xining City, Qinghai Province is one catty in 42 yuan, and one catty in 40 yuan is lower than that in 42 yuan. Therefore, 40 yuan a catty of sheep hind legs is not expensive in Xining City, Qinghai Province.