# Pre Calculus 12

posted by .

Solving problems that involve logarithms

the sound at a rock concert decreases by 10% for every 5m travvelled. how far does it take for a volume of 2000 decibels to decrease to 20 decibels?

i don't know what to do for this one
the growth decay formula i got is

A = P(X)^t/n

I don't know what to do. Can someone please explain step by step?

• Pre Calculus 12 -

In your formula, you don't define X, t, and n
but I am guessing it would be

20 = 2000(.9)^(t/5) ,.... ( .9 because if it decreases by 10% it would leave 90% or .9)
.01 = .9^(t/5)
log both sides

log .01 = log .9^(t/5
-2 = (t/5) log.9
t/5 = -2/log.9 = 43.70869..
t = 218.54 m

• Pre Calculus 12 -

how do i log both sides? divide by 2000 on both sides?

• Pre Calculus 12 -

I first of all divided both sides by 2000 to get
.01 = .9^(t/5)

then log both sides

log (.01) = log (.9^(t/5) )

taking the log is a mathematical operation just like multiplying, taking square roots or adding
remember, whatever we do to one side, we must do to the other side.

• Pre Calculus 12 -

thanks soo much Reiny :) You are such a great math helper on here! :D

## Similar Questions

1. ### Math

Find the number of decibels for the power of the sound. Round to the nearest decibel. A rock concert, 5.19 10-6 watts/cm2 D= ?
2. ### algebra

Find the number of decibels for the power of the sound. Round to the nearest decibel. A rock concert, 5.4 10-6 watts/cm2
3. ### Algebra II

1. A sound has an intensity of 5.92 „e 1025W/m2.What is the loudness of the sound in decibels?
4. ### algebra

Find the number of decibels for the power of the sound. round to the nearest decibel. A rock concert, 5.35x 10^4 watts/cm^2
5. ### Algebra

Find the number of decibels for the power of the sound. Round to the nearest decibel. A rock concert, 5.3 10-6 watts/cm2
6. ### algebra

find the number of decibels for the power of the sound. round to nearest decibel. a rock concert 5.34*10^-6 watts/cm^2 D= Db
7. ### Math

Find the number of decibels for the power of the sound. Round to the nearest decibel. A rock concert, 5.35 10-6 watts/cm2 D =______ dB
8. ### Algebra

Find the number of decibels for the power of the sound. Round to nearest decibels. A rock concert, 5.21 x 10^-6watts/cm^2 D= dB
9. ### PreCalculas

The psychological sensation of loudness B is measured in decibels and is defined with reference to the intensity, , of a barely audible sound by the following equation. In this equation, I is the intensity of the sound in question. …
10. ### LOGS

The decibel level of a sound is given by dB=10log(EE0), where E0=10−12wattsm2 and E is the intensity of the sound. (a) Find the intensity of a 80-decibel sound. E= watts per square meter. (b) How many times more intense is the …

More Similar Questions