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6.Interest
hard
In how many $years$ will a sum of ₹ $800$ at $10 \%$ per annum compounded semi-annually become ₹ $926.10$?
A
$1.33$
B
$1.5$
C
$2.33$
D
$2 .5$
Solution
Let the required number of years be $N$.
$\therefore \quad 800\left(1+\frac{10}{200}\right)^{2 N}=926.10$
i.e. $\quad 800\left(\frac{105}{100}\right)^{2 N}=926.10$
$800\left(\frac{21}{20}\right)^{2 N}=926.10$
$\therefore$
$\begin{aligned}\left(\frac{21}{20}\right)^{2 N} &=\frac{926.10}{800} \\&=\frac{9261}{8000} \\&=\left(\frac{21}{20}\right)^{3}\end{aligned}$
$\therefore$
$2 N=3$ years
or $N=1 \frac{1}{2}$ years
Standard 13
Quantitative Aptitude
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