Given:
A sum of money doubles itself in 20 years.
Concept Used:
Simple Interest, SI =\(P\; \times\; R \; \times T\over 100\)
Calculation:Let's assume sum of money = P
So, Simple interest = P ( Because P + P =2P in 20 years)
⇒ P =\(P\; \times\; R \; \times 20\over 100\)
⇒ 20 R = 100
⇒ R = 5%
∴A sum of money doubles itself in 20 years in simple interestat 5% interest rate.