Let's assume that students who like both subjects account for X.

The formula is 3/4+4/5-x= 1- 1/20.

The solution is x=3/5.

Analysis: On the left are those who like mathematics and those who like Chinese, which includes the repetition of two subjects. Subtract repetition and include all uninterested students except two subjects (that is, those who like Chinese and mathematics, those who only like Chinese and those who only like mathematics).

On the right is everyone minus people who are not interested in these two subjects, that is, counting students who are not interested except two subjects is equal to the left.

Equation: (3/4+4/5)-(1-1/20) = 3/5.

In the same way; In a similar way