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

Respond to this Question

First Name
School Subject
Your Answer

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