The intensity of a 70-dB whistle is quintupled. What is the new decibel level?

Question

Quizplus · Accepted Answer

The decibel scale is logarithmic, which means that an increase in intensity of 10 times is equal to an increase of 10 dB. Therefore, to quintuple the intensity (increase by a factor of 5), we need to add 10 dB, twice:

Original intensity: 70 dB 
Increase by 10 dB: 80 dB 
Increase by another 10 dB: 90 dB 
Dropping the last digit (which is less than 5) gives an answer of 82 dB.

The Intensity of a 70-DB Whistle Is Quintupled