$\"\"$

\

Find intesity of auditrium when the level of sound is $\"\"$ .

\

The equation of level of sound is $\"\"$ , where $\"\"$ is an intesity of $\"\"$ .

\

Substitute $\"\"$ and $\"\"$ in $\"\"$ .

\

$\"\"$

\

Product property of logarithm : $\"\"$ .

\

$\"\"$

\

Power property of logarithm : $\"\"$ .

\

$\"\"$

\

Apply property of logarithm : $\"\"$ .

\

$\"\"$

\

$\"\"$

\

Defnition of logarithm : $\"\"$ if and only if $\"\"$ .

\

$\"\"$ .

\

Intesity of auditrium when the level of sound $\"\"$ is $\"\"$ .

\

$\"\"$

\

Find intesity of auditrium when the level of sound is $\"\"$ .

\

Substitute $\"\"$ and $\"\"$ in $\"\"$ .

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

Intesity of auditrium when the level of sound $\"\"$ is $\"\"$ .

\

The percentage of decrease in the intensity : $\"\"$ .

\

$\"\"$

\

Therefore, the percentage of decrease in the noise due to the material is $\"\"$ .

\

$\"\"$

\

The percentage of decrease in the noise due to the material is $\"\"$ .