In how many years will a certain sum of money double itself at 5% Simple Interest?

Correct option is D

Formula Used:
S.I =P $$\times$$​ r$$\times$$ t/100
Calculation:
Let the time period be 't' years and the sum(principal) be 'P',amount = 2P, S.I = 2P - P = P, rate = 5% p.a.
P = P $$\times$$5$$\times$$​t/100
=> t = 20 years
required time = 20 years