Question

At what rate of simple interest will a sum of money double itself in 20 years?

Answer 1

$A=P+SI$

$\Rightarrow 2P=P+SI$ so $SI=P$

$SI=\frac{PRT}{100}$

$\Rightarrow P=\frac{P\times R\times 20}{100}$

$\Rightarrow R=\frac{100}{20}=5\%$