Justin School had 500 pupils and Fabian School had 10% more pupils. When an equal number of pupils left each school, the ratio of the pupils in Fabian School to that in Justin School became 5 : 4. How many pupils were there in both schools in the end?

	Justin School	Fabian School	Difference
Before	500		50
Change	- ?	- ?
After	5 u	4 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 Justin School and Fabian School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 10% x 500
= ¹⁰₁₀₀ x 500
= 50

Difference between the number of pupils in both schools in the end
= 5 u - 4 u
= 1 u

1 u = 50

Total number of pupils in both schools in the end
= 5 u + 4 u
= 9 u
= 9 x 50
= 450

Answer(s): 450