Carl School had 576 pupils and Daniel School had 25% less pupils. When an equal number of pupils joined each school, the ratio of the pupils in Daniel School to that in Carl School became 5 : 4. How many pupils were there in both schools in the end?

	Carl School	Daniel School	Difference
Before	576		144
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 Carl School and Daniel School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 25% x 576
= ²⁵₁₀₀ x 576
= 144

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

1 u = 144

Total number of pupils in both schools in the end
= 5 u + 4 u
= 9 u
= 9 x 144
= 1296

Answer(s): 1296