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SSC Sample Paper Mock Test-7 SSC CGL Tear-II Paper-1

  • question_answer
    A sum of money invested at compound interest doubles itself in 6 yr. At the same rate of interest it will amount to eight times of itself in

    A)  15 yr

    B)  12 yr   

    C)  18 yr   

    D)  10 yr

    Correct Answer: C

    Solution :

    Let the sum be Rs. x. Then,    \[2x=x{{\left( 1+\frac{r}{100} \right)}^{6}}\]\[\Rightarrow \]\[2={{\left( 1+\frac{r}{100} \right)}^{6}}\] Cubing both sides, \[8={{\left\{ {{\left( 1+\frac{r}{100} \right)}^{6}} \right\}}^{3}}\]\[\Rightarrow \]\[8={{\left( 1+\frac{r}{100} \right)}^{18}}\] \[\Rightarrow \]\[8x=x{{\left( 1+\frac{r}{100} \right)}^{18}}\] \[\therefore \] The sum will be 8 times in 18 yr


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