Question
The simple interest on a certain sum of money at the rate of 5% p.a. for 8 years is Rs. 840. At what rate of interest the same account of interest can be received on the same sum after 5 years?
Answer: Option B
$$\eqalign{
& {\text{S}}{\text{.I}}{\text{.}} = {\text{Rs}}{\text{. 840}} \cr
& {\text{R}} = {\text{5}}\% \cr
& {\text{T}} = 8\,{\text{years}} \cr
& {\text{Principal}} \cr
& = {\text{Rs}}{\text{. }}\left( {\frac{{100 \times 840}}{{5 \times 8}}} \right) \cr
& = {\text{Rs}}{\text{.}}\,2100 \cr
& {\text{Now,}} \cr
& {\text{P}} = {\text{Rs}}{\text{.}}\,2100 \cr
& {\text{S}}{\text{.I}}{\text{.}} = {\text{Rs}}{\text{.}}\,{\text{840}} \cr
& {\text{T}} = {\text{5 years}}{\text{}} \cr
& \therefore {\text{Rate}} \cr
& = \left( {\frac{{100 \times 840}}{{2100 \times 5}}} \right)\% \cr
& = {\text{8}}\% \cr} $$
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$$\eqalign{
& {\text{S}}{\text{.I}}{\text{.}} = {\text{Rs}}{\text{. 840}} \cr
& {\text{R}} = {\text{5}}\% \cr
& {\text{T}} = 8\,{\text{years}} \cr
& {\text{Principal}} \cr
& = {\text{Rs}}{\text{. }}\left( {\frac{{100 \times 840}}{{5 \times 8}}} \right) \cr
& = {\text{Rs}}{\text{.}}\,2100 \cr
& {\text{Now,}} \cr
& {\text{P}} = {\text{Rs}}{\text{.}}\,2100 \cr
& {\text{S}}{\text{.I}}{\text{.}} = {\text{Rs}}{\text{.}}\,{\text{840}} \cr
& {\text{T}} = {\text{5 years}}{\text{}} \cr
& \therefore {\text{Rate}} \cr
& = \left( {\frac{{100 \times 840}}{{2100 \times 5}}} \right)\% \cr
& = {\text{8}}\% \cr} $$
Was this answer helpful ?
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