A person invested Rs. 2,000 on simple interest for 7 years to obtain a total amount of Rs. 3,400 on a certain annual rate of interest. What was the rate of interest to obtain the above amount ?
3 men can do as much work as 5 boys. The wages of 3 boys are equal to those of 2 men. A piece of work for which 40 boys and 15 men are employed takes 8 weeks and costs Rs 15750. How long would it take if 20 boys and 20 men were employed and how much would it cost?