While tabulation of marks scored in an examination by the students of a class, by mistake the marks scored by one student

While tabulation of marks scored in an examination by the students of a class, by mistake the marks scored by one student got recorded as 93 in place of 63, and thereby the average marks increased by 0.5. What was the number of students in the class?

(a) 20

(b) 60

(c) 30

(d) 15

Sol:

Increment of 30 marks, results in 0.5 increment in average

⇒30/x = 0.5

=>x=60