Question

at what rate of simple interest will be a sum double itself in 10
 years ?

Answer 1

let rate = r 
let initial amount  = p
final amount = 2p

             use formula,
S.I = p × r × t/100
final amount = intial amount  + S.I
                2p = p + p × r × 10/100
                p = pr/10
                r = 10 %