Billy School had 310 pupils and Zane School had 40% less pupils. When an equal number of pupils joined each school, the ratio of the pupils in Zane School to that in Billy School became 5 : 4. How many pupils were there in both schools in the end?

	Billy School	Zane School	Difference
Before	310		124
Change	+ ?	+ ?
After	5 u	4 u	1 u

Since an equal number of pupils joined 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 Billy School and Zane School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 40% x 310
= ⁴⁰₁₀₀ x 310
= 124

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

1 u = 124

Total number of pupils in both schools in the end
= 5 u + 4 u
= 9 u
= 9 x 124
= 1116

Answer(s): 1116