How many people where there in Hall B after the change?

Question

In Hall A, 30%of the 800 people were men. In Hall B, 40%of the 400 people were women and children. After some of the peole in both halls had switched hall, 25% of the people in Hall A and 75% of those in Hall B were men. How many people were there in Hall B after the change?

Answer 1

an algebra question where you have to use X and Y and solve two equations at the same time.

the answer is

A = 840

B = 360