Given: A sum of money (P) doubles in 10 years Formula Used: Simple interest =
PTR
100
Amount = P + Interest Where, P = Principle, R = Rate, T = Time period Calculation: According to the question Amount after 10 years = 2P So, Simple Interest = A - P ⇒ Simple interest = 2P - P = P ⇒P×R×
10
100
=P R = 10% When time is 20 years ⇒ Simple interest =R×T×
P
100
⇒ Simple interest =10×20×
P
100
⇒ Simple interest = 2P ⇒ Amount = P + 2P = 3P ∴ The amount after 20 years would be 3P.