Logarithmic applications help

spoc21

Hi, I am having a lot of trouble solving the following three logarithmic application problems..I would greatly appreciate any help that you guys might offer. I am only allowed to use logarithmic/exponential equations here.

[FONT=&quot]1. If a car depreciates at 15% per year, how long is it until it is worth half its original value?

2. [FONT=&quot] Led Zeppelin once played a concert which exerted sounds of 10,000 times the intensity of a sound that can just be heard. What is the loudness in decibels?

3.
[FONT=&quot]A radioactive substance that has a half-life of 8 days is to be temporarily implanted in a hospital patient until three-fifths of the amount originally present remains. How long should the implant remain in the patient?
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Thanks
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pickslides

MHF Helper
[FONT=&quot]1. If a car depreciates at 15% per year, how long is it until it is worth half its original value?

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$$\displaystyle \frac{1}{2}= 0.85^n$$

solve for $$\displaystyle n$$

spoc21

spoc21

$$\displaystyle \frac{1}{2}= 0.85^n$$

solve for $$\displaystyle n$$

Thanks pickslides..I'm good with this one, and the car depreciation one. However, I'm still very confused by the Led Zeppelin one. I would greatly appreciate any helpful tips/suggestions that you might offer.