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Bunuel looks like D and E have the exact same value?
\(400 * 8^{1/36} = 25 * 2^4 * (2^3)^{1/36} = 25 * 2^4 * 2^{1/12} = 25 * 2^{49/12} \)


Bunuel
Jennifer invests $2,000 at an annual interest rate of r% compounded quarterly for 9 years. At the end of 9 years her account is worth $16,000. What is the value of r?


A. \(400(2\cdot4^{\frac{1}{9}}-1)\)

B. \(25(2^{\frac{25}{36}}-1)\)

C. \(100\cdot8^{\frac{1}{9}}-1\)

D. \(25\cdot2^{\frac{49}{12}}-400\)

E. \(400\cdot8^{\frac{1}{36}}-400\)
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Bunuel
Jennifer invests $2,000 at an annual interest rate of r% compounded quarterly for 9 years. At the end of 9 years her account is worth $16,000. What is the value of r?


A. \(400(2\cdot4^{\frac{1}{9}}-1)\)

B. \(25(2^{\frac{25}{36}}-1)\)

C. \(100\cdot8^{\frac{1}{9}}-1\)

D. \(25\cdot2^{\frac{49}{12}}-400\)

E. \(400\cdot8^{\frac{1}{36}}-200\)


The formula for Amount(A) in case of compound interest = \(P* (1 + \frac{r}{(n*100)})^{n*t}\)
where P is the principal amount, r is the rate of interest, t is the time in years and n is the number of times the interest in applied in a year.
In this question:
A = $ 16,000
P = $ 2,000
n = 4 (since we are compounding quaterly)
t = 9 years

So, we can write:
    \(16,000 = 2,000 * (1 + \frac{r}{(4*100)})^{4*9}\)
    \(8 = (1 + \frac{r}{400})^{36}\)

    \(1+ \frac{r}{400} = 8^{\frac{1}{36}}\)

    \(r = 400*2^{\frac{3}{36}} - 400\)

    \(r = 25*2^4*2^{\frac{1}{12}} - 400\)

    \(r = 25*2^{\frac{49}{12}} - 400\)

Thus, the correct answer is Option D.
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