Question

At what rate percent per year will a sum double itself in 25/4 years?si

Answer 1

Let the principal be Rs.x
Time=25/4 years.
Amount=2*x=2x
Interest=A-P=2x-x=x
Using SI=P*R*T/100,we get
R=100*SI/(P*T)
or,R=100*x/(x*25/4)
or,R=100*4*x/25x
or,R=16
Answer:It will double itself in 25/4 years(6 years 3 months) at 16% p.a.

Answer 2

Simple interest case:

Sum doubles if Sum = Principal + interest  = 2 P   => interest = principal

      Interest = principal = P = P r t       = >   r t  = 1

            r = 1/t = 4/25 or  (4/25) * 100% = 16% per year