Charlie School had 500 pupils and Reggie School had 10% more pupils. When an equal number of pupils left each school, the ratio of the pupils in Reggie School to that in Charlie School became 2 : 1. How many pupils were there in both schools in the end?

	Charlie School	Reggie School	Difference
Before	500		50
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 Charlie School and Reggie 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
= 2 u - 1 u
= 1 u

1 u = 50

Total number of pupils in both schools in the end
= 2 u + 1 u
= 3 u
= 3 x 50
= 150

Answer(s): 150