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