A invest of Rs. P in compound interest (compound half yearly) at 20% p. a. for one year. He received interest for Rs. 378. If he invests Rs. P+400 in simple interest at 12% p. a. for three years, then find the difference between P/2 and the simple interest he received after three years.

Correct option is C

​$$\text{Composite compound interest} = \left(10 + 10 + \frac{10 \times 10}{100} \right)\% = 21\%\\[10pt]\text{ATQ,}\\[5pt]P \times \frac{21}{100} = 378\\[5pt]P = 1800\\[10pt]\text{Amount invested on simple interest} = \text{Rs. } P + 400 \\[5pt]= 1800 + 400 = \text{Rs. } 2200\\[10pt]\text{Simple interest} = 2200 \times 12 \times \frac{3}{100} = \text{Rs. } 792\\[10pt]\text{Required difference} = \frac{1800}{2} - 792 = 108$$​​