Question

When required the following logarithms may be used.
$\log 2=.3010300,\log 3=.4771213$,
$\log 7=.8450980,\log 11=1.0413927$.
In how many years will a sum of money double itself at $5$ per cent. compound interest?

Answer 1

$A=P{(1+\frac{R}{100})}^n$

As the money needs to be doubled so $A=2P$

$\Rightarrow 2={1.05}^n$

$\Rightarrow \log 2=n\log 1.05$

$\Rightarrow n=\frac{\log 2}{\log 1.05}=14.2$ years.