For class A:
Total students=25
Students passed with first class=20
So fraction of students in class A who passed with first class = students passed with first class/total students
Therefore ,Fraction=20/25=4/5
For class B:
Total Students=30
Students passed with first class=24
So fraction of students in class A who passed with first class = students passed with first class/total students
Therefore ,Fraction=24/30=4/5
Hence the both classes have equal fraction of those students who passed with first class.