"In 2015
Let students appeared in exam B = a
Students appeared in exam A = 2a
Students appeared in exam C = a – 40
So a + 2a + a – 40 = 1640
4a = 1680
a = 420
Students appeared in exam B = 420
Students appeared in exam A = 840
Students appeared in exam C = 380
In 2017:
Let students appeared in exam A and exam B be 7c and 9c respectively.
Students appeared in exam C = 125% of 9c = 11.25c
So 7c + 9c + 11.25c = 2180
27.25c = 2180
c = 80
Students appeared in exam A = 560
Students appeared in exam B = 720
Students appeared in exam C = 900
Number of students appeared in exams B and C together in 2015 = 420 + 380 = 800
Number of students appeared in exams A and B together in 2017 = 560 + 720 = 1280
Difference = 1280 – 800 = 480
Hence, option B is correct."