Kavita has a cumulative time deposit account in a bank. She deposits ₹800 per month and gets ₹16,700 as maturity value. If the rate of interest be 5% per annum, find the total time for which the account was held. (Hint: x² + 481x − 10020 = 0 ⇒ x² + 501x − 20x − 10020 = 0)

David opened a recurring deposit account in a bank and deposited ₹300 per month for two years. If he received ₹7,725 at the time of maturity, find the rate of interest per annum.

Rekha opened a recurring deposit account for 20 months. The rate of interest is 9% per annum and Rekha receives ₹441 as interest at the time of maturity. Find the amount Rekha deposited each month.

Mr. Sonu has a recurring deposit account and deposits ₹750 per month for 2 years. If he gets ₹19,125 at the time of maturity, find the rate of interest.