Correct Answer - Option 3 : 8%

**Given**

Compound interest = Rs.3328

Simple interest = Rs.3200

**Formula used**

C.I - S.I = (R × S.I)/(2 × 100)

Where C.I, S.I and R is compound interest, simple interest and rate of interest respectively,

**Calculation**

128 = (R × 3200)/(2 × 100)

⇒ (128 × 2 × 100)/3200 = R

⇒ 8% = R

**∴ Rate is 8% per annum.**