Correct Answer - Option 3 : 50%

**Given:**

A sum of money becomes 11 times of principal

Time = 20 years

**Formula Used:**

Simple Interest = Amount - Principal

Simple Interest = (Principal × Rate × Time)/100

**Calculation:**

Let the Principal be P

Then Amount after 20 years will be 11P

Simple Interest = 11P - P = 10P

10P = (P × Rate × 20)/100

⇒ Rate = 50%

**∴ The Rate of interest per annum is 50%**