I tried solving this question by taking values,
As ques is asking whether B > 20, Let us consider B =20 so that we can check if value satisfies if not then would be sufficient or insufficient accordingly
Now A+B > 120
Statement 1 :
(1) If number of students in classroom A are doubled and number of students in classroom B are halved, the difference between the number of students in classroom A and B is less than 200.
Min No of students considered in B =20, A : 101 == > A+B =121
Now A is doubled: 202, B is halved, B= 10
A- B :192 : less than 200 as required,
Now if we go less than 20, all values will satisfy , Now let us check if B> 20 also satisfy this
b= 22, A =102 : A+ B =124
Doubling A = 204, B = 1/2 *22 =11
A- B = 193,
Still satisfies equation,
Thus B < 20 and B> 20 both possible,
Insufficient
Statement 2 :
(2) If 20 students from each classroom leave the school, the sum of number of students in both classes would be more than 80.
So min no of Students in B = 20 , Because they leave school .
Now A+ B > 120 from initial stem
A+B- 40 > 80
A+B > 120
It can be that A has all the students and B has 20 or B can have more than 20 also.
So B > 20
In sufficient
Combining we know that Min no of students B has is 20, But as we checked 20 also satisfies statement 1 and statement 2 and B > 20 also satisfies,
Still Insufficient.
IMO E
i know this might not be correct algebric method, but tried using numbers