Answer
$3$
Work Step by Step
Recall:
(1) $\log_a{b}+\log_a{c}=\log_a{\left(bc\right)}$
(2) $n\cdot \log_a{b}=\log_a{\left(b^n\right)}$
Use rule (2) above to obtain:
\begin{align*}
2\log5+\log{40}&=\log{5^2}+\log{40}\\
&=\log{25}+\log{40}
\end{align*}
Use rule (1) above to obtain:
\begin{align*}
\log{25}+\log{40}&=\log{(25\cdot 40)}\\
&=\log{1000}\\
&=\log{10^3}
\end{align*}
Recall:
$\log{10^n} = n$
Thus,
$\log{10^3}=3$
