A pupil's marks were wrongly entered as 79 instead of 45. Due to that the average marks for the class got increased by half. The number of pupils in the class is : Pick one.
A) 30 B) 80 C) 20 D) 68 E) 26

Rationale: "let there be x pupils in the class . total increase in marks = ( x * 1 / 2 ) = x / 2 . x / 2 = ( 79 - 45 ) = > x / 2 = 34 = > x = 68 . answer : d"
Answer: D