Compound Interest - Aptitude MCQ Questions and Solutions with Explanations

$$\eqalign{ & 28.90 = x{\left( {\frac{{8.5}}{{100}}} \right)^2} \cr & 28.90 = \frac{{x \times 8.5 \times 8.5}}{{10000}} \cr & 1.7 = \frac{{x \times 0.5 \times 8.5}}{{10000}} \cr & 0.1 \times 10000 = x \times 0.5 \times 0.5 \cr & x = {\text{Rs}}{\text{. }}4000 \cr} $$

$${\text{Rate }}\% = \frac{{60}}{5} = 12\% $$

$$159 \to 159 \times 10 = 1590$$

5% = $$\frac{1}{{20}}$$
\[\begin{array}{*{20}{c}} {}&{{\text{Principal}}}&{}&{{\text{Installment}}}&{} \\ {{{\text{I}}^{{\text{st}}}}{\text{ year}} \to }&{{{20}_{ \times 21}}}&:&{{{21}_{ \times 21}}}&{} \\ {{\text{I}}{{\text{I}}^{{\text{nd}}}}{\text{ year}} \to }&{400}&:&{441}&{ \to 44100} \end{array}\]
1 unit → 100
Principal = 400 + 420 = 820
Total installment = 441 × 2 = 882
Interest = 882 - 820
= 62 × 100   [1 unit = 100]
= 6200

\[\left. \begin{gathered} {\text{Rate of interest}} = 6\% {\text{ year}} \hfill \\ {\text{Rate of interest}} = 8\% {\text{ year}} \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 4\% {\text{ half year}} \hfill \\ {\text{Net rate}} = 4 + 4 + \frac{{16}}{{100}} = 8.16\% \hfill \\ \end{gathered} \right)\begin{array}{*{20}{c}} {2.16\mu \to 10800} \\ {1\mu \to 50} \\ {100\mu \to {\mathbf{5000}}} \end{array}\]

$$\eqalign{ & 7562\,\_\_\_\_\_\_\_\_\,8469.44 \cr & {\text{Rate of interest}} = \frac{{907.44}}{{7562}} \times 100 = 12\% \cr} $$

Amount in 2 years $$ \to 12000 \times \frac{6}{5} \times \frac{6}{5} = 17280$$

$$ \Rightarrow {\text{Rate}} = \frac{1}{1} \times 100 = 100{\text{ Answer}}$$

\[P = 10500\xrightarrow{{\,\,\,\,\,2{\text{ year}}\,\,\,\,\,}}13650\]
$$\eqalign{ & 2{\text{ year}} \to 3150 \cr & 3150 = \frac{{10500 \times R \times 2}}{{100}} \cr & R = 15\% \cr & A = 10500{\left( {1 + \frac{{15}}{{200}}} \right)^2} \cr & = 10500 \times \frac{{215 \times 215}}{{200 \times 200}} \cr & = \frac{{105 \times 43 \times 43}}{{16}} \cr & = 12134 \cr} $$