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Sarah invested $8,000\$8,000 in a savings account. After 1010 years, her investment grew to $12,000\$12,000. What is the annual interest rate, compounded continuously, that Sarah's account earned? Round your answer to the nearest two decimal places in percentage form. Use the formula A=PertA = Pe^{rt}, where AA is the balance (final amount), PP is the principal (starting amount), ee is the base of natural logarithms (2.71828\approx 2.71828), rr is the interest rate expressed as a decimal, and tt is the time in years.

Full solution

Q. Sarah invested $8,000\$8,000 in a savings account. After 1010 years, her investment grew to $12,000\$12,000. What is the annual interest rate, compounded continuously, that Sarah's account earned? Round your answer to the nearest two decimal places in percentage form. Use the formula A=PertA = Pe^{rt}, where AA is the balance (final amount), PP is the principal (starting amount), ee is the base of natural logarithms (2.71828\approx 2.71828), rr is the interest rate expressed as a decimal, and tt is the time in years.
  1. Identify Values: Identify the given values: A = $12,000\$12,000 P = $8,000\$8,000 t = 1010 \text{ years} Use the formula A=PertA = Pe^{rt}.
  2. Rearrange Formula: Rearrange the formula to solve for rr: A=PertA = Pe^{rt} 12,000=8,000imese10r12{,}000 = 8{,}000 imes e^{10r} Divide both sides by 8,0008{,}000: rac{12{,}000}{8{,}000} = e^{10r} 1.5=e10r1.5 = e^{10r}
  3. Take Natural Logarithm: Take the natural logarithm (\ln) of both sides to solve for r r : ln(1.5)=ln(e10r) \ln(1.5) = \ln(e^{10r}) ln(1.5)=10r \ln(1.5) = 10r
  4. Isolate rr: Divide both sides by 1010 to isolate rr:\newliner=ln(1.5)/10r = \ln(1.5) / 10
  5. Calculate r: Calculate the value of rr:\newlinerln(1.5)/10r \approx \ln(1.5) / 10\newliner0.4055/10r \approx 0.4055 / 10\newliner0.04055r \approx 0.04055
  6. Convert to Percentage: Convert rr to a percentage: r0.04055×100r \approx 0.04055 \times 100 r4.06%r \approx 4.06\%

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