If $\log 2=0.30103$ then the number of digits in $5^{20}$ is

$\begin{array}{l}\log 5^{20}=20\log 5=20\times \log \left(\frac{10}{2}\right)\\ =20(\log 10-\log 2)\\ =20(1-0.30103)\\ =20\times 0.6990=13.9800\end{array}$

Characteristic $=13$

Hence the number of digits in $5^{20}$ is 14