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:
20
80
100
200
Explanation:
Let the number of students in rooms A and B be $ x $ and $ y $ respectively.
Then, $ x $ - 10 = $y $ + 10 $\Rightarrow$ $ x $ - $ y $ = 20 .... (i)
and $ x $ + 20 = 2$\left( y - 20\right)$ $\Rightarrow$ $ x $ - 2$ y $ = -60 .... (ii)
Solving (i) and (ii) we get: $ x $ = 100 , $ y $ = 80.
$\therefore$ The required answer A = 100.