The average weight of the students in four sections A, B, C and D is 60 kg. The average weight of the students of A, B, C and D individually are 45 kg, 50 kg, 72 kg and 80 kg, respectively. If the average weight of the students of section A and B together is 48 kg and that of B and C together is 60 kg. What is the ratio of the number of the students in sections A and D ?

• A. 12 : 7
• B. 4 : 3
• C. 3 : 2
• D. 8 : 5