The difference between the compound interest and simple interest on some amount of money for 2 years at 9% per annum is Rs.129.60. The sum of money is - किसी धनराशि पर 9% वार्षिक दर से 2 वर्ष के चक्रवृद्धि तथा साधारण ब्याजों का अंतर 129.60 रू. है, वह धनराशि है -

The difference between compound and simple interest for 2 years at rate r percent is given by the formula P times (r over 100) squared. Substituting 129.60 equals P times (9 over 100) squared gives P equals 129.60 times 10000 over 81 equals 16000. This works because compound interest earns interest on interest while simple interest does not.