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.