Simplification question for IBPS, SBI, RBI, PO, UPSC, State-PSC, Railways, SSC

[Q] 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:
(a) 450
(b) 200
(c) 350
(d) 100

Solution

Answer    (d)
Explanation
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Let the number of students in rooms A and B be x and y respectively.
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 required answer A = 100.