Correct me if I'm wrong, but...
If there are 500 million cats in the world and one meow's intensity level L(1)=65dB, the correct answer should be around 150dB. Why? Because intensity level is logarithmic and here's the solution: L=10xlog(I/I0) in which I0=10^-12W/m^2. We get one meow's intensity I(1)=3,16...x10^-6W/m^2. If there are 500 million cats, the total intensity I(tot)=500x10^6x3,16...x10^-6=1581,1...W/m^2.
The total intensity level L(tot) is then 152dB.
If there are 500 million cats in the world and one meow's intensity level L(1)=65dB, the correct answer should be around 150dB. Why? Because intensity level is logarithmic and here's the solution: L=10xlog(I/I0) in which I0=10^-12W/m^2. We get one meow's intensity I(1)=3,16...x10^-6W/m^2. If there are 500 million cats, the total intensity I(tot)=500x10^6x3,16...x10^-6=1581,1...W/m^2.
The total intensity level L(tot) is then 152dB.