A man gave 50% of his saving of Rs. 84100 to his wife and divided the remaining sum among his two sons A and B of 15 years 13 years of age respectively. he divided it in such a way that each of his sons, when they attain the age of 18 years would receive the same amount at 5% compound interest per annum. The Share of B was :

After giving 50% to wife, remaining amount = Rs. 42050. Son A (15 years) gets amount P_A, son B (13 years) gets amount P_B. A invests for 3 years (until 18), B invests for 5 years (until 18). At 5% CI: P_A(1.05)^3 = P_B(1.05)^5. Solving: P_A/P_B = (1.05)^5/(1.05)^3 = (1.05)^2 = 1.1025. Also P_A + P_B = 42050. Substituting: 1.1025P_B + P_B = 42050, so 2.1025P_B = 42050, giving P_B ≈ Rs. 20000.