Tom School had 610 pupils and Billy School had 40% less pupils. When an equal number of pupils joined each school, the ratio of the pupils in Billy School to that in Tom School became 4 : 3. How many pupils were there in both schools in the end?

	Tom School	Billy School	Difference
Before	610		244
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 Tom School and Billy School at first and in the end the same. 

Difference between the number of pupils in both schools at first
= 40% x 610
= ⁴⁰₁₀₀ x 610
= 244

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

1 u = 244

Total number of pupils in both schools in the end
= 4 u + 3 u
= 7 u
= 7 x 244
= 1708

Answer(s): 1708