A sum of Rs. 20000 is invested for three years at compound interest. The rate of interest for first year is 20 percent per annum, for second year it is 15 percent per annum and for third years it is 10 percent per annum. Find the interest for the third year.

For 1^st year, R% = 20% Amount = 20000 × [(1 + (20/100)] => 20000 × [1 + (1/5)] => 20000 × (6/5) = 24000 Compound Interest = 24000 – 20000 = Rs.4000 For 2^nd year, P = Rs.24000 and R% = 15% Amount = 24000 × [(1 + (15/100)] => Amount = 24000 × (23/20) = 1200 × 23 = Rs.27600 Compound Interest = 27600 – 24000 = Rs.3600 For 3rd year, P = Rs. 27600, R% = 10%, Amount = 27600 × [(1 + (10/100)] = 27600 × (11/10) = 2760 × 11 = Rs. 30360 Compound Interest = 30360 – 27600 = Rs.2760