Answer:
12 machines
Explanation:
[tex]I_0[/tex] = Threshold of sound = [tex]10^{-12}\ W/m^2[/tex]
[tex]90=10log\dfrac{I}{I_0}\\\Rightarrow 9=log\dfrac{I}{10^{-12}}\\\Rightarrow 10^9=\dfrac{I}{10^{-12}}\\\Rightarrow I=10^9\times 10^{-12}\\\Rightarrow I=10^{-3}\ W/m^2[/tex]
[tex]92=10log\dfrac{I}{I_0}\\\Rightarrow 9.2=log\dfrac{I}{10^{-12}}\\\Rightarrow 10^{9.2}=\dfrac{I}{10^{-12}}\\\Rightarrow I=10^{9.2}\times 10^{-12}\\\Rightarrow I=10^{-2.8}\ W/m^2[/tex]
One machine makes
[tex]I_m=\dfrac{10^{-2.8}}{32}=0.0000495279122644\ W/m^2[/tex]
Number of machines
[tex]n=\dfrac{10^{-3}}{\dfrac{10^{-2.8}}{32}}=20.19\approx 20\ machines[/tex]
Number of machines that are needed to be removed = 32-20 = 12 machines
