A loan of Rs. 305 was taken at a certain rate per annum of compound interest, for 3 years. After 3 years the amount repaid was Rs. 670, calculate the rate of compound interest.
18 men or 36 boys working 6 hours a day can plough a field in 24 days. In how many days will 24 men and 24 boys working 9 hours a day plough the same field ?