UPSC NDA Math Model Paper 5

Given the avg. marks of boys = 52 and that of girls = 42
Let the no. of boys be x and of girls be y
Sum of marks of boys = 52 x
Sum of marks of girls = 42 y
According to the question, if 50 is the combined average;
⇒ 52x + 42y = 50(x + y)
⇒ 52x + 42y = 50x + 50y
⇒ 2x = 8y
∴ x = 4y
Total number of students in the class = x + y = 4y + y = 5y
% of boys =frac‌

No of boys

Total No. of students

×100
=

4y

5y

×100
=80%