Question

find the compound interest at the rate of 10% per annum for three years on the principal which,in three years,at the rate of rate of 4% per annum gives RS 1,200 as simple interest.

Answer 1

Dear student,
$$\begin{gathered} LetPrincipalbeRsP \\ RateR=4\% \\ Timen=3yrs \\ SI=Rs1200 \\ WeknowSI=\frac{PRT}{100} \\ \Rightarrow 1200=\frac{P\times 4\times 3}{100} \\ \Rightarrow P=\frac{1200\times 100}{4\times 3} \\ \Rightarrow P=\frac{100\times 100}{1} \\ \Rightarrow P=Rs10,000 \\ TofindCIwehave, \\ P=Rs10000 \\ R=10\% \\ n=3yrs \\ weknowA=P{\left(1+\frac{R}{100}\right)}^n \\ A=10000{\left(1+\frac{10}{100}\right)}^3 \\ A=10000\times \frac{11}{10}\times \frac{11}{10}\times \frac{11}{10} \\ A=10\times 1331 \\ A=Rs13310 \\ Now,CI=A-P \\ CI=13310-10000 \\ CI=Rs3310 \end{gathered}$$
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