Correct Answer - Option 1 : 5%

**Given**

Simple interest = (1/5) of the sum

Time = 4 years

**Formula used**

Rate = (simple interest × 100)/(p × 4)

Where, p, r and t are principal, rate and time respectively

**Calculation**

Rate = [(1/5)P × 100]/(p × 4)

⇒ Rate = 20/4

⇒ Rate = 5%

**∴ Rate of interest is 5%.**