Rs.125 becomes Rs.216 in three years at compound interest. The rate of interest per annum is:

20% 12% 25% 15%

20%

In 3 years : Principal : Amount = 125 : 216 = (5)3 : (6)3 In 1 year : Principal : Amount = \(\sqrt[3]{5^3 }\) : \(\sqrt[3]{6^3 }\) = 5 : 6 Interest = 6 - 5 = 1R Interest rate = \(\frac{1}{5}\) × 100% = 20%