David School had 390 pupils and Ben School had 30% more pupils. When an equal number of pupils left each school, the ratio of the pupils in Ben School to that in David School became 3 : 2. How many pupils were there in both schools in the end?

	David School	Ben School	Difference
Before	390		117
Change	- ?	- ?
After	3 u	2 u	1 u

Since an equal number of pupils left each school, the difference in the number of pupils at first and in the end between the 2 schools remains the same.  Make the difference between the number of pupils in David School and Ben School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 30% x 390
= ³⁰₁₀₀ x 390
= 117

Difference between the number of pupils in both schools in the end
= 3 u - 2 u
= 1 u

1 u = 117

Total number of pupils in both schools in the end
= 3 u + 2 u
= 5 u
= 5 x 117
= 585

Answer(s): 585