Oscar School had 350 pupils and Vincent School had 30% less pupils. When an equal number of pupils joined each school, the ratio of the pupils in Vincent School to that in Oscar School became 4 : 3. How many pupils were there in both schools in the end?

	Oscar School	Vincent School	Difference
Before	350		105
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 Oscar School and Vincent School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 30% x 350
= ³⁰₁₀₀ x 350
= 105

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

1 u = 105

Total number of pupils in both schools in the end
= 4 u + 3 u
= 7 u
= 7 x 105
= 735

Answer(s): 735