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A huge ice glacier in the Himalayas initially covered an area of 45 square kilometers. Because of changing weather patterns, this glacier begins to melt, and the area it covers begins to decrease exponentially.
The relationship between 
A, the area of the glacier in square kilometers, and 
t, the number of years the glacier has been melting, is modeled by the following equation.

A=45e^(-0.05 t)
How many years will it take for the area of the glacier to decrease to 15 square kilometers?
Give an exact answer expressed as a natural logarithm.
years

A huge ice glacier in the Himalayas initially covered an area of 4545 square kilometers. Because of changing weather patterns, this glacier begins to melt, and the area it covers begins to decrease exponentially.\newlineThe relationship between A A , the area of the glacier in square kilometers, and t t , the number of years the glacier has been melting, is modeled by the following equation.\newlineA=45e0.05t A=45 e^{-0.05 t} \newlineHow many years will it take for the area of the glacier to decrease to 1515 square kilometers?\newlineGive an exact answer expressed as a natural logarithm.\newlineyears

Full solution

Q. A huge ice glacier in the Himalayas initially covered an area of 4545 square kilometers. Because of changing weather patterns, this glacier begins to melt, and the area it covers begins to decrease exponentially.\newlineThe relationship between A A , the area of the glacier in square kilometers, and t t , the number of years the glacier has been melting, is modeled by the following equation.\newlineA=45e0.05t A=45 e^{-0.05 t} \newlineHow many years will it take for the area of the glacier to decrease to 1515 square kilometers?\newlineGive an exact answer expressed as a natural logarithm.\newlineyears
  1. Rephrase the Question: First, let's rephrase the "How many years will it take for the area of the glacier to decrease to 1515 square kilometers?"
  2. Given Exponential Decay Model: We are given the exponential decay model for the area of the glacier as a function of time: A=45e0.05tA = 45e^{-0.05t}. We need to find the value of tt when A=15A = 15 square kilometers.
  3. Set AA equal to 1515: To find tt, we set AA equal to 1515 and solve for tt:15=45e(0.05t)15 = 45e^{(-0.05t)}
  4. Isolate Exponential Term: Divide both sides of the equation by 4545 to isolate the exponential term:\newline1545=e0.05t\frac{15}{45} = e^{-0.05t}
  5. Simplify Left Side: Simplify the left side of the equation: 13=e0.05t\frac{1}{3} = e^{-0.05t}
  6. Take Natural Logarithm: Take the natural logarithm of both sides to solve for tt:ln(13)=ln(e0.05t)\ln(\frac{1}{3}) = \ln(e^{-0.05t})
  7. 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(13)=0.05t\ln(\frac{1}{3}) = -0.05t
  8. Divide by 0.05-0.05: Divide both sides by 0.05-0.05 to solve for tt:t=ln(13)0.05t = \frac{\ln(\frac{1}{3})}{-0.05}

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