At what rate of simple interest per year will a sum of money double itself in 20 years?

💡 Solution & Explanation

To double, the interest must equal the principal, which is 100% of it. That 100% is earned over 20 years, so the yearly rate = 100 ÷ 20 = 5%. Check with ₹100: 5% for 20 years gives ₹100 of interest, making ₹200.