(b) Let the initial students in class be 2x, 3x and 4x Now, when 40 is added in each class. New, number of students will be 4y, 5y and 6y. Now, according to the question 2x + 40 = 4y ..........(i) 3x + 40 = 5y .........(ii) and 4x + 40 = 6y ......(iii) ∴ On solving above equations 2x = 40 ∴x = 20 Hence, total number of students= 2x + 3x + 4x = 9x = 9 x 20 = 180 students