John's marks wrongly entered as 82 instead of 62. Due to that the average marks for the class got increased by half (1/2). The number of John in the class is? Choose the correct choice from the following answers:
A) 70
B) 78
C) 80
D) 84
E) 90

Rationale: otal increase in marks = x x 1 = x 2 2 x / 2 = ( 82 - 62 ) x / 2 = 40 x = 80 . c
Answer: C