Seth School had 510 pupils and Jeremy School had 30% less pupils. When an equal number of pupils joined each school, the ratio of the pupils in Jeremy School to that in Seth School became 4 : 3. How many pupils were there in both schools in the end?

	Seth School	Jeremy School	Difference
Before	510		153
Change	+ ?	+ ?
After	4 u	3 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 Seth School and Jeremy School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 30% x 510
= ³⁰₁₀₀ x 510
= 153

Difference between the number of pupils in both schools in the end
= 4 u - 3 u
= 1 u

1 u = 153

Total number of pupils in both schools in the end
= 4 u + 3 u
= 7 u
= 7 x 153
= 1071

Answer(s): 1071