There are some pupils seated in the auditorium. When 8 girls stand up, the number of girls who are seated becomes 3/4 of the number of boys who are seated. When 8 boys stand up, the number of boys who are seated becomes 11/10 of the number of girls who are seated. How many pupils are there in the auditorium?
Assuming that the two actions are independently done,
g-8 = 3/4 b
b-8 = 11/10 g
solve for b and g, and then you want b+g to get the total students who started out seated. (That does not count any who might not have been seated to start with, but were in the auditorium.)