A sum of money doubles itself in 8 years at simple interest. What is the rate of interest per annum?

यदि मूलधन (P) दोगुना हो जाता है, तो ब्याज (I) = P। सूत्र I = PRT/100 का उपयोग करते हुए: P = (P * R * 8) / 100 => 100 = 8R => R = 12.5%।