Ian School had 675 pupils and Andy School had 20% more pupils. When an equal number of pupils left each school, the ratio of the pupils in Andy School to that in Ian School became 2 : 1. How many pupils were there in both schools in the end?

	Ian School	Andy School	Difference
Before	675		135
Change	- ?	- ?
After	2 u	1 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 Ian School and Andy School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 20% x 675
= ²⁰₁₀₀ x 675
= 135

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

1 u = 135

Total number of pupils in both schools in the end
= 2 u + 1 u
= 3 u
= 3 x 135
= 405

Answer(s): 405