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:  Pick one.
A) 20 B) 80 C) 100 D) 200 E) 250
Explanation:   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.   Answer: 100
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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: