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6.Interest
hard
Sonika invested an amount of ₹ $5800$ for $2$ years. At what rate of compound interest ($\%$ $per$ $annum$) will she get an amount of ₹ $594.5$ at the end of two years?
A
$5$
B
$4$
C
$6$
D
$8$
Solution
(a) $594.5=5800\left[\left(1+\frac{r}{100}\right)^{2}-1\right]$
$\frac{594.5}{5800}=\left(1+\frac{r}{100}\right)^{2}-1$
$0.1025+1=\left(1+\frac{r}{100}\right)^{2}$
$1.1025=\frac{(100+r)^{2}}{10000}$
$1.1025 \times 10000=(100+r)^{2}$
$11025=(100+r)^{2}$
$(105)^{2}=(100+r)^{2}$
$105=100+r$
$r=5 \%$
Standard 13
Quantitative Aptitude
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