In how many years will a sum of money doubles itself at 5% per annum simple interest  Pick:
A) 25 years
B) 28 years
C) 10 years
D) 20 years
E) 21 years
let the initial sum be x   then,Amount=2x(because sum will be double)   Amount = Principal + S.I   2x = x + s.I   S.I = x   S.I = (p*r*t)/100   x = (x*5*t)/100   therefore,t = 20 years   ANSWER:20 years
<result>D</result>
In how many years will a sum of money doubles itself at 5% per annum simple interest