Let:

• P = Principal amount
• r = Rate of interest per year
• t = Time in years

We know that the amount doubles in 5 years. So, the amount (A) after 5 years will be 2P.

The formula for simple interest is: A = P + (P * r * t)

Substituting the given values: 2P = P + (P * r * 5)

Simplifying the equation: 2P - P = 5Pr P = 5Pr

Divide both sides by P: 1 = 5r

Solving for r: r = 1/5 = 0.2

To express this as a percentage, multiply by 100: r = 0.2 * 100 = 20%

Therefore, the rate of simple interest is 20% per year.