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6.Interest
medium
A sum of money borrowed and paid back in two annual instalments of ₹ $882$ each allowing $5 \%$ compound interest. The sum (In ₹) borrowed was
A
$1620$
B
$1640$
C
$1680$
D
$1700$
Solution
Annual instalment $=₹ 882, R =5 \%$
$\therefore \quad$ Required amount $=\frac{882}{\left(1+\frac{5}{100}\right)^{2}}+\frac{882}{\left(1+\frac{5}{100}\right)}$
i.e., Amount borrowed $=\frac{882}{\left(\frac{21}{20}\right)^{2}}+\frac{882}{\left(\frac{21}{20}\right)}$
$=882\left[\left(\frac{20}{21}\right)^{2}+\left(\frac{20}{21}\right)\right]=882\left[\frac{20^{2}+20 \times 21}{21^{2}}\right]$
$=2[400+420]=₹ 1640$
Standard 13
Quantitative Aptitude
