Given: The total numbers of students in sections A and B of a class are 72. The ratio of the number of students in A and B is 7 : 5. The average weight (in kg) of the students in section B is 20% more than that of the students in section A. The average weight of all the students in the class is 52 kg, Formula used: Average = sum of observations/Number of observations Calculation: The number of students = 72 Number of students in section A = 72 × (7/12) = 42 Number of students in section B = 72 – 42 = 30 Let the average weight of section A be 5x Average weight of section B = 5x × (6/5) = 6x According to the question 42 × 5x + 30 × 6x = 72 × 52 210x + 180x = 3744 390x = 3744 x = 3744/390 = 9.6 Average weight of students in section B = 6x = 6 × 9.6 = 57.6 ∴ The average weight (in kg) of the students in section B is 57.6. Alternate Solution: Let the number of students in sections A and B are 7 and 5 respectively. Let the average weight of section A be 5x. Average weight of section B = 5x × (6/5) = 6x According to the question 7 × 5x + 5 × 6x = 12 × 52 35x + 30x = 12 × 52 65x = 12 × 52 x = (12 × 52)/65 = 9.6 Average weight of section B = 9.6 × 6 = 57.6