Question

At what rate percent will a sum treble itself in $20years$?

Answer 1

Let $P$ be the principal.

$$\begin{gathered} A=3P \\ SI=3P-P=2P \\ T=20years \\ R=\frac{SI\times 100}{P\times T}=\frac{2P\times 100}{P\times 20}=10years \end{gathered}$$