Question

At what rate percent per annum will sum of money double in 8 years​

Answer 1

Let principal = P, Then, S.I.= P and Time = 8 years  

We know that S.I. = P x T x R/100                          

Rate = [(100 x P)/ (P x 8)]% = 12.5% per annum.

Answer 2

let the principal amount be Rs. 100

$= > 100 \times rate \times 8 = 200 \\ \\ = > rate = \frac{200}{800} \\ \\ = > rate = \frac{1}{4} \\ \\ = > rate = \frac{1}{4} \times 100\% \\ \\ = > rate = 25\%$