Seth invested a certain amount of money and got back an amount of ₹8400. If the bank paid an interest of ₹700, find the amount Seth invested.
Alex’s father invested some amount of money in the bank on simple interest. The amount grew to ₹36,000 at the end of 2 years. He waited for another 5 years and got a final amount of ₹51,000. What was the principal amount that he invested at the beginning?