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You invested $5,000\$5,000 in a savings account, and after 1010 years, the balance grew to $8,144\$8,144. The interest is compounded annually. What is the annual interest rate? Use the formula A=P(1+rn)ntA = P\left(1 + \frac{r}{n}\right)^{nt}, where AA is the balance (final amount), PP is the principal (starting amount), rr is the interest rate expressed as a decimal, nn is the number of times per year that the interest is compounded, and tt is the time in years. Round your answer to the nearest tenth.

Full solution

Q. You invested $5,000\$5,000 in a savings account, and after 1010 years, the balance grew to $8,144\$8,144. The interest is compounded annually. What is the annual interest rate? Use the formula A=P(1+rn)ntA = P\left(1 + \frac{r}{n}\right)^{nt}, where AA is the balance (final amount), PP is the principal (starting amount), rr is the interest rate expressed as a decimal, nn is the number of times per year that the interest is compounded, and tt is the time in years. Round your answer to the nearest tenth.
  1. Identify values: Identify the values of AA, PP, nn, and tt. A=$8,144A = \$8,144 P=$5,000P = \$5,000 n=1n = 1 (compounded annually) t=10t = 10 years
  2. Substitute values: Substitute the values into the formula A=P(1+rn)ntA = P\left(1 + \frac{r}{n}\right)^{nt}. 8,144=5,000(1+r1)1108,144 = 5,000\left(1 + \frac{r}{1}\right)^{1 \cdot 10}
  3. Simplify equation: Simplify the equation. 8,144=5,000(1+r)10 8,144 = 5,000(1 + r)^{10}
  4. Divide sides: Divide both sides by 5,0005,000 to isolate (1+r)10(1 + r)^{10}. (1+r)10=8,1445,000(1 + r)^{10} = \frac{8,144}{5,000} (1+r)10=1.6288(1 + r)^{10} = 1.6288
  5. Take 1010th root: Take the 1010th root of both sides to solve for (1+r)(1 + r). 1+r=(1.6288)(1/10)1 + r = (1.6288)^{(1/10)} 1+r1.05001 + r \approx 1.0500
  6. Subtract to solve: Subtract 11 from both sides to solve for rr. r1.05001r \approx 1.0500 - 1 r0.0500r \approx 0.0500
  7. Convert to percentage: Convert rr to a percentage.
    r0.0500×100%r \approx 0.0500 \times 100\%
    r5.0%r \approx 5.0\%

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