This is a typical problem of chickens and rabbits in the same cage. You can assume that 10kg of tea comes from 50 yuan, so suppose that 500 yuan is 2 10 yuan less than the actual 7 10 yuan. This is because a part of every kilogram of tea in 80 yuan was replaced by every kilogram of tea in 50 yuan. How much was it replaced? Divide 2 10 by (50-30) to get 7 kilograms, which is the replacement amount, that is, 7 kilograms per kilogram of tea in 80 yuan ~

Of course, the most direct method is to set two variables to solve two equations at the same time.