If a sum of Rs. 3600 is invested in two different banks for two years first offering 20% compound interest compounded annually and second offers 20% compound interest compounded half yearly. Then find the difference of their interest after two years?

First bank: Annual compounding at 20% for 2 years on Rs. 3600. Amount = 3600 × (1.2)² = 3600 × 1.44 = Rs. 5184. Interest = 5184 - 3600 = Rs. 1584. Second bank: Half-yearly compounding means 10% per half-year for 4 periods. Amount = 3600 × (1.1)⁴ = 3600 × 1.4641 = Rs. 5270.76. Interest = 5270.76 - 3600 = Rs. 1670.76. Difference = 1670.76 - 1584 = Rs. 86.76 ≈ Rs. 86.76.