A recurring deposit of Rs. 10 is paid regularly each month for 24 months, and amounts to Rs. 257.50. what is the rate of interest? रू. 10 की आवर्ती जमा राशि 24 माह के लिए प्रत्येक माह में नियमित रूप से भुगतान की जाती है और 257.50 के बराबर है। ब्याज की दर क्या है?

For a recurring deposit, maturity value M = P×n + P×n(n+1)/2×r/12×1/100 where P is monthly installment, n is number of months, r is annual rate. Here: P = 10, n = 24, M = 257.50. Principal deposited = 10×24 = 240. Interest = 257.50 - 240 = 17.50. Using the formula: I = P×n(n+1)/2×r/12×1/100, we get 17.50 = 10×24×25/2×r/12×1/100. Solving: 17.50 = 25r, so r = 0.70 or 7%.