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

Explanation

Let Principal = P. Amount = 2P, so Simple Interest (SI) = 2P – P = P. Using SI = (P × R × T) / 100, we get P = (P × R × 8) / 100. Solving for R gives R = 100 / 8 = 12.5% per annum.