Question
Rs.2000 amounts to Rs. 2226.05 in 2 years at compound interest. What will be the rate of interest ?
Answer: Option C
$$\eqalign{
& {\text{Let the rate be R}}\% {\text{ p}}{\text{.a}}{\text{.}} \cr
& {\text{Then,}} \cr
& {\text{2000}}{\left( {1 + \frac{{\text{R}}}{{100}}} \right)^2} = 2226.05 \cr
& \Rightarrow {\left( {1 + \frac{{\text{R}}}{{100}}} \right)^2} = \frac{{222605}}{{200000}} \cr
& \, \Rightarrow {\left( {1 + \frac{{\text{R}}}{{100}}} \right)^2} = \frac{{44521}}{{40000}} \cr
& \Rightarrow {\left( {1 + \frac{{\text{R}}}{{100}}} \right)^2} = {\left( {\frac{{221}}{{200}}} \right)^2} \cr
& \Rightarrow 1 + \frac{{\text{R}}}{{100}} = \frac{{211}}{{200}} \cr
& \Rightarrow \frac{{\text{R}}}{{100}} = \frac{{11}}{{200}} \cr
& \Rightarrow {\text{R}} = \frac{{11}}{2}\% \cr
& \Rightarrow {\text{R}} = 5.5\% \cr} $$
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$$\eqalign{
& {\text{Let the rate be R}}\% {\text{ p}}{\text{.a}}{\text{.}} \cr
& {\text{Then,}} \cr
& {\text{2000}}{\left( {1 + \frac{{\text{R}}}{{100}}} \right)^2} = 2226.05 \cr
& \Rightarrow {\left( {1 + \frac{{\text{R}}}{{100}}} \right)^2} = \frac{{222605}}{{200000}} \cr
& \, \Rightarrow {\left( {1 + \frac{{\text{R}}}{{100}}} \right)^2} = \frac{{44521}}{{40000}} \cr
& \Rightarrow {\left( {1 + \frac{{\text{R}}}{{100}}} \right)^2} = {\left( {\frac{{221}}{{200}}} \right)^2} \cr
& \Rightarrow 1 + \frac{{\text{R}}}{{100}} = \frac{{211}}{{200}} \cr
& \Rightarrow \frac{{\text{R}}}{{100}} = \frac{{11}}{{200}} \cr
& \Rightarrow {\text{R}} = \frac{{11}}{2}\% \cr
& \Rightarrow {\text{R}} = 5.5\% \cr} $$
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