Answer
$\log{10,000}=4$
Work Step by Step
Let
$x=\log{10,000}.$
RECALL:
$\log{y} = b \longleftrightarrow 10^b = y.$
Use the definition above to convert the equation to an exponential equation and have
$10^x=10,000.$
Write each side in base 10 to have
$10^x=10^4.$
The bases are the same, so the exponents must be equal. Thus,
$x=4.$
Therefore $\log{10,000}=4$.