Question

You hear sounds at the following decibel levels: 5 dB, 10 dB, 20 dB, and 40 dB. Which sound is 10 times higher than the lowest pressure humans can hear?
40 dB
10 dB
20 dB
5 dB

Answer 1

The lowest pressure the human can hear is 20 micro Pa or 20x10^-6 Pa.
to convert it dB = 20 log ( p / p0 )
where p is the pressure you want to hear
p0 is the lowest pressure the human can hear

since you want 10 times higher the lowest possible
p/p0 = 10
dB = 20 log ( 10 )
dB = 20 dB