Question

3/4 of seats in a concert hall were occupied. The ratio of adults to children was 7:3. If 90 more adults attended the concert, the number of adults would be 3 times of number of children. How many seats were in the concert hall?

Answer 1

we have
a/c = 7/3
a+90 = 3c

a = 315
c = 135

but, that's only 3/4 of the seats, so the total is

4/3 (315+135) = 600

Answer 2

600

Answer 3

540