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Ksivusya [100]
3 years ago
10

Sum of $1000 was invested for 4 years, and the interest was compounded semiannually. If this sum amounted to $1389.08 in the giv

en time, what was the interest rate? Please round your answer to two decimal places.
Mathematics
1 answer:
eduard3 years ago
7 0
The answer is 8%

Compound interest formula is:
A = P(1 + r/n)ⁿˣ
A - the final amount
P - the initial amount
r - interest rate
n - number of compoundings per year
x - time period

We have:
A = <span>$1389.08
P = </span><span>$1000
r = ?
n = 2  (it is semiannual)
x = 4

</span>A = P(1 + r/n)ⁿˣ
1389.08 = 1000(1 + r/2)²*⁴
1389.08 = 1000(1 + r/2)⁸
(1 + r/2)⁸ = 1389.08/1000
(1 + r/2)⁸ = 1.389
\sqrt[8]{(1 +  \frac{r}{2} ) ^{8}}   =  \sqrt[8]{1.389}  \\ &#10;1 +  \frac{r}{2} =1.04 \\ &#10; \frac{r}{2} = 1.04-1 \\ &#10; \frac{r}{2} = 0.04 \\ &#10;r = 2*0.04 =0.08
r = 0.08 = 8/100 = 8%
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