ब्याज की दर (% प्रति वर्ष में) क्या है यदि किसी निश्चित राशि पर तीसरे वर्ष में अर्जित साधारण ब्याज 20 रुपये है और 2 वर्षों में अर्जित चक्रवृद्वि ब्याज 41.60 रुपये है?

A sum becomes 25 times of itself when invested for 48 years at r% simple interest per annum. Find the compound interest earned if Rs. 51,200 is invested at r% per annum when interest is compounded half-yearly, for 1.5 years.

Simple interest on a certain sum at 4% per annum for 2 years is ₹80. What is the compound interest on the same sum for the same period at the same rate?