Fraction word problem

Question

3/5 of the pupils in Class A and 3/7 of the pupils in class B are girls. The two classes had the same number of boys. What fraction of the total number of pupils are boys from Class B?

Answer 1

4/7 are boys from class B

we can say (2/5)A = (4/7)B where A and B are the total number of students in classes A and B respectively.