Dylan School had 780 pupils and Tim School had 10% more pupils. When an equal number of pupils left each school, the ratio of the pupils in Tim School to that in Dylan School became 5 : 4. How many pupils were there in both schools in the end?

	Dylan School	Tim School	Difference
Before	780		78
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 Dylan School and Tim School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 10% x 780
= ¹⁰₁₀₀ x 780
= 78

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

1 u = 78

Total number of pupils in both schools in the end
= 5 u + 4 u
= 9 u
= 9 x 78
= 702

Answer(s): 702