According to the question, 9000 – 6000 = (6000 × r × 24) ÷ (12 × 100) Or, 3000 = 120 × r Or, r = 25 When the sum is invested at compound interest, Effective rate of interest = (r + 20) ÷ 3 = (25 + 20) ÷ 3 = 15% Effective time period = 1 × 3 = 3 units Amount received = Principal × {1 + (r/100)}time period = 6000 × {1 + (15/100)}3 = 6000 × (1.15)3 = 9125.25