What is the decibel level

On a workday the average decibel level of a
busy street is 69 dB, with 125 cars passing a
given point every minute.
If the number of cars is reduced to 39 cars
every minute on a weekend, what is the decibel level of the street?
Answer in units of dB.

I think I know how your teach wants this done, but the problem is weird, as averaging decibel levels is pretty meaningless, since they are logs.

ratio of cars is 39/125 = 0.312

now you can change the dB to a ratio and multiply, but it's easier to change 0.312 to a dB and subtract.
0.312 = –5.06 dB
69 dB – 5.06 dB = 63.94 dB

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