Glen School had 690 pupils and Seth School had 20% more pupils. When an equal number of pupils left each school, the ratio of the pupils in Seth School to that in Glen School became 4 : 3. How many pupils were there in both schools in the end?

	Glen School	Seth School	Difference
Before	690		138
Change	- ?	- ?
After	4 u	3 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 Glen School and Seth School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 20% x 690
= ²⁰₁₀₀ x 690
= 138

Difference between the number of pupils in both schools in the end
= 4 u - 3 u
= 1 u

1 u = 138

Total number of pupils in both schools in the end
= 4 u + 3 u
= 7 u
= 7 x 138
= 966

Answer(s): 966