The average marks of 60 students in a class is 60. If the average marks of boys and girls in the class are 54 and 72 respectively, then find the difference between the number of boys and girls in the class.

Correct option is E

Information Given:
The average marks of 60 students in a class is 60.
The average marks of boys and girls in the class are 54 and 72 respectively .
Formulas Used:
Total marks = Average marks × Total number of students
Total marks = (Number of boys × Average of boys) + (Number of girls × Average of girls)
Basic Explanation:
Total marks = 60×60=3600
Let total boys be b and total girls 60 – b.
ATQ,
b × 54 + (60 - b) × 72 = 3600
54b + 4320 – 72b = 3600
720 = 18b
40 = b
The total boys = 40
And total girls = 60 – 40 = 20
Required difference = 40 – 20 = 20

Exam Hall Method: