Question

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. 20
• B. 80
• C. 100
• D. 200

Answer 1

The correct option is C 100

Let the number of students in rooms A and B be x and y respectively.
Then, $x-10=y+10\Rightarrow x-y=\mathrm{20....}\left(i\right)$
and $x+20=2(y-20)\Rightarrow x-2y=-60....\left(ii\right)$
Solving (i) and (ii) we get: $x=100,y=80.$
$\therefore$ The required answer $A=100.$