Ken School had 390 pupils and Lee School had 40% less pupils. When an equal number of pupils joined each school, the ratio of the pupils in Lee School to that in Ken School became 5 : 4. How many pupils were there in both schools in the end?

	Ken School	Lee School	Difference
Before	390		156
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 Ken School and Lee School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 40% x 390
= ⁴⁰₁₀₀ x 390
= 156

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

1 u = 156

Total number of pupils in both schools in the end
= 5 u + 4 u
= 9 u
= 9 x 156
= 1404

Answer(s): 1404