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A large brine tank containing a solution of salt and water is being diluted with fresh water.
The relationship between the elapsed time, 
t, in hours, after the dilution begins, and the concentration of salt in the tank, 
S(t), in grams per liter 
(g//l), is modeled by the following function.

S(t)=600*e^(-0.3 t)
How many hours will it take for the concentration of salt to decrease to 
100g//l ?
Round your answer, if necessary, to the nearest hundredth.
hours

A large brine tank containing a solution of salt and water is being diluted with fresh water.\newlineThe relationship between the elapsed time, t t , in hours, after the dilution begins, and the concentration of salt in the tank, S(t) S(t) , in grams per liter (g/l) (\mathrm{g} / \mathrm{l}) , is modeled by the following function.\newlineS(t)=600e0.3t S(t)=600 \cdot e^{-0.3 t} \newlineHow many hours will it take for the concentration of salt to decrease to 100 g/l 100 \mathrm{~g} / \mathrm{l} ?\newlineRound your answer, if necessary, to the nearest hundredth.\newlinehours

Full solution

Q. A large brine tank containing a solution of salt and water is being diluted with fresh water.\newlineThe relationship between the elapsed time, t t , in hours, after the dilution begins, and the concentration of salt in the tank, S(t) S(t) , in grams per liter (g/l) (\mathrm{g} / \mathrm{l}) , is modeled by the following function.\newlineS(t)=600e0.3t S(t)=600 \cdot e^{-0.3 t} \newlineHow many hours will it take for the concentration of salt to decrease to 100 g/l 100 \mathrm{~g} / \mathrm{l} ?\newlineRound your answer, if necessary, to the nearest hundredth.\newlinehours
  1. Write Function and Concentration: Write down the given function and the concentration level we want to find the time for.\newlineWe have the function S(t)=600e0.3tS(t) = 600 \cdot e^{-0.3t} and we want to find the time tt when S(t)=100S(t) = 100 g/l.
  2. Set Up Equation: Set up the equation to solve for tt when S(t)=100S(t) = 100.100=600e0.3t100 = 600 \cdot e^{-0.3t}
  3. Isolate Exponential Term: Divide both sides of the equation by 600600 to isolate the exponential term.\newline100600=e(0.3t) \frac{100}{600} = e^{(-0.3t)} \newline16=e(0.3t) \frac{1}{6} = e^{(-0.3t)}
  4. Take Natural Logarithm: Take the natural logarithm of both sides to solve for tt.ln(16)=ln(e0.3t)\ln(\frac{1}{6}) = \ln(e^{-0.3t})
  5. Simplify Right Side: Use the property of logarithms that ln(ex)=x\ln(e^x) = x to simplify the right side of the equation.ln(16)=0.3t\ln(\frac{1}{6}) = -0.3t
  6. Divide by 0.3 -0.3 : Divide both sides by 0.3 -0.3 to solve for t t .t=ln(16)0.3 t = \frac{\ln(\frac{1}{6})}{-0.3}
  7. Calculate Value of t: Calculate the value of t using a calculator.\newlinetln(16)0.3ln(0.1666666667)0.33.52636052t \approx \frac{\ln(\frac{1}{6})}{-0.3} \approx \frac{\ln(0.1666666667)}{-0.3} \approx 3.52636052
  8. Round to Nearest Hundredth: Round the answer to the nearest hundredth.\newlinet3.53t \approx 3.53 hours

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