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A new car is purchased for 18600 dollars. The value of the car depreciates at 
14% per year. To the nearest tenth of a year, how long will it be until the value of the car is 6800 dollars?
Answer:

A new car is purchased for 1860018600 dollars. The value of the car depreciates at 14% 14 \% per year. To the nearest tenth of a year, how long will it be until the value of the car is 68006800 dollars?\newlineAnswer:

Full solution

Q. A new car is purchased for 1860018600 dollars. The value of the car depreciates at 14% 14 \% per year. To the nearest tenth of a year, how long will it be until the value of the car is 68006800 dollars?\newlineAnswer:
  1. Identify type of depreciation: Determine the type of depreciation.\newlineThe car depreciates at a constant percentage each year.\newlineThis is an example of exponential decay.
  2. Find initial value, rate, final value: Identify the initial value aa, the rate of depreciation rr, and the final value P(t)P(t).\newlineInitial value aa = $18,600\$18,600\newlineRate of depreciation rr = 14%14\% per year or 0.140.14 as a decimal\newlineFinal value P(t)P(t) = $6,800\$6,800
  3. Set up exponential decay formula: Set up the exponential decay formula.\newlineThe formula for exponential decay is P(t)=a(1r)tP(t) = a \cdot (1 - r)^t, where P(t)P(t) is the value after time tt, aa is the initial value, and rr is the rate of decay.
  4. Plug in known values: Plug in the known values into the exponential decay formula.\newline6800=18600×(10.14)t6800 = 18600 \times (1 - 0.14)^t
  5. Solve for t: Solve for t.\newlineFirst, divide both sides by $18,600\$18,600 to isolate the exponential part of the equation.\newline$6,800/$18,600=(10.14)t\$6,800 / \$18,600 = (1 - 0.14)^t\newline0.3655913978494624=0.86t0.3655913978494624 = 0.86^t
  6. Take natural logarithm: Take the natural logarithm of both sides to solve for tt.ln(0.3655913978494624)=ln(0.86t)\ln(0.3655913978494624) = \ln(0.86^t)
  7. Use logarithm property: Use the property of logarithms that ln(ab)=bln(a)\ln(a^b) = b \cdot \ln(a).ln(0.3655913978494624)=tln(0.86)\ln(0.3655913978494624) = t \cdot \ln(0.86)
  8. Divide by ln(0.86)\ln(0.86): Divide both sides by ln(0.86)\ln(0.86) to solve for tt.\newlinet=ln(0.3655913978494624)ln(0.86)t = \frac{\ln(0.3655913978494624)}{\ln(0.86)}
  9. Calculate value of t: Calculate the value of t using a calculator.\newlinetln(0.3655913978494624)ln(0.86)t \approx \frac{\ln(0.3655913978494624)}{\ln(0.86)}\newlinet7.267t \approx 7.267
  10. Round to nearest tenth: Round the answer to the nearest tenth of a year.\newlinet7.3t \approx 7.3 years

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