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The question is:

The noise from a vacuum cleaner is 85 dB while that from a television set is 78 dB. What is the intensity level of the two sounds together?

i can't find the right formula.

thanks.

jeo
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    You convert both to power (in Watt, horsepower, pirate-ninjas, or whatever your favourite denomination is), you add them together, and then you convert back into dB. – Arthur Sep 14 '15 at 05:45
  • i still cant answer. – jeo Sep 14 '15 at 05:57

2 Answers2

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The formula is $$10\log(10^{[\text{dB of sound 1}]/10} + 10^{\text{[dB of sound2]}/10})$$ where Log(x) is the base-10 logarithm. Plugging in your numbers we get $85.790097$ dB

Arthur
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Brevan Ellefsen
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Hint:

dBs are logarithmic and so can't be manipulated directly.

Express them on a linear scale, do the addition and then covert back to dB.

Bangkockney
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