Dipu Babu’s total interest for 1 year
= (\frac{15000 × 5}{100} × \frac{3}{12}+\frac{12000 × 5}{100} × \frac{3}{12}+\frac{20000 × 5}{100} × \frac{6}{12}) \\
= ₹ (\frac{150 × 5}{4}+150+500)
= ₹ 187.50 +₹ 150 +₹ 500 = ₹ 837.50
∴ His amount will be ₹ [20000+837.50]= ₹ 20837.50