Question

At what rate of simple interest will a some of money double itaself in 20 years

Answer 1

let sum be x

amount = double of sum

interest= P*R*T/100

            =x*R*20/100      

            =Rx/5

amount = interest + sum

        2 x = Rx/5 + x

        2 x= Rx + 5 x / 5

      2 x * 5 = Rx + 5 x

           10 x =Rx + 5x

      10 x - 5 x = R x

               5 x = R x

            5 x /x = R

            5 % = R