Question

IB exams

There are two examinations rooms A and B. If 10 students are sent from A to B, then the number of students in each room is the same. If 20 candidates are sent from B to A, then the number of students in A is double the number of students in B.The number of students in room A is ?

Answer 1

Let us consider that the number of students in rooms A and B be x and y 
Then, x - 10 = y + 10      x - y = 20 .... (i)   
  and x + 20 = 2(y - 20)      x - 2y = -60 ....
(ii)Solving (i) and (ii)
we get: x = 100 , y = 80.
The number of students in room A is = 100.