The simple interest on a sum of money for 3 years is Rs.240 and the compound interest on the same sum at the same rate for 2 years is Rs.70 less than the given simple interest. The sum of money is - एक धनराशि पर 3 वर्ष में साधारण ब्याज 240 रू. है और उसी धनराशि पर उसी ब्याज दर से 2 वर्ष में चक्रवृद्धि ब्याज दिए गए साधारण ब्याज से 70 रू. कम है। धनराशि है -

SI for 3 years = 240, so SI for 1 year = 80. CI for 2 years = 240 - 70 = 170. Let principal = P, rate = r%. SI for 2 years = 2Pr/100 = 160 (since SI for 3 years = 240). So Pr = 8000. CI for 2 years = P(1 + r/100)² - P = 170. Using approximation: CI ≈ SI for 2 years + interest on first year's interest. First year interest = 80, second year interest on 80 = 80r/100. CI = 160 + 80r/100 = 170, so 80r/100 = 10, r = 12.5%. Then Pr = 8000 means P × 12.5 = 8000, P = 640. The claimed answer D is correct.