Answer
10 times.
Work Step by Step
The decibel scale is logarithmic, based upon powers of 10. Adding 10 dB means the intensity is multiplied by a factor of 10. In other words, when the intensity of sound is increased by a factor of 10, the intensity level increases by 10 dB.
A sound of 40 dB is ten times more intense than a sound of 30 dB.
This is discussed on page 394, and shown in Table 21.1.
