4. The average marks obtained in a class of 50 students is 70%. The average of first 25 is 60% and that of 24 is 80%. What is the marks obtained by the last student?
8. A trader buys 800 kgs of tomatoes for Rs 7200. 10% tomatoes are damaged in transportaion. At what rate (Rs/Kg) should he sell the rest to earn 30% profit?