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Lucas invested $5,000\$5,000 in an account to save for a trip abroad. After 77 years, his investment grew to $15,000\$15,000. What is the annual interest rate, compounded continuously, that Lucas's account earned?? \newlineUse 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.\newlineRound your answer to the nearest two decimal places in percentage form.

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Q. Lucas invested $5,000\$5,000 in an account to save for a trip abroad. After 77 years, his investment grew to $15,000\$15,000. What is the annual interest rate, compounded continuously, that Lucas's account earned?? \newlineUse 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.\newlineRound your answer to the nearest two decimal places in percentage form.
  1. Identify Values: Identify the values for AA, PP, and tt.
    A = $15,000\$15,000
    P = $5,000\$5,000
    t = 77 years
  2. Use Formula: Use the formula A=PertA = Pe^{rt}.\newline Substitute A=15,000A = 15,000, P=5,000P = 5,000, and t=7t = 7.\newline 15,000=5,000×e7r15,000 = 5,000 \times e^{7r}
  3. Isolate e7re^{7r}: Divide both sides by 5,0005{,}000 to isolate e7re^{7r}.\newline 15,0005,000=e7r\frac{15{,}000} {5{,}000} = e^{7r}\newline 3=e7r3 = e^{7r}
  4. Take Natural Logarithm: Take the natural logarithm (ln\ln) of both sides to solve for rr.\newline ln(3)=ln(e7r)\ln(3) = \ln(e^{7r})\newline ln(3)=7r\ln(3) = 7r
  5. Divide by 77: Divide both sides by 77 to solve for rr. \newliner=ln(37)r = \ln(\frac{3} {7}) r0.15694r \approx 0.15694
  6. Convert to Percentage: Convert rr to a percentage by multiplying by 100100.\newline r0.15694×100r \approx 0.15694\times 100 r15.7%r \approx 15.7\%So, the annual interest rate Lucas's account earned is approximately 15.7%15.7\%.

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