8th Class Mathematics Comparing Quantities Question Bank Comparing Queantities

  • question_answer Peter invested a certain sum of money in a simple interest bond whose value grew to Rs. 600 at the end of 6 years, and to Rs. 800 at the end of another 10 years. What was the rate of interest?

    A)  12%                            

    B)  16.66%

    C)  18.67%                       

    D)  19.25%

    Correct Answer: B

    Solution :

    (b): Let rate of interest be 'r' sum invested = P \[\therefore 600=P\left( 1+\frac{6r}{100} \right).......1\] and  \[800=P\left( 1+\frac{10r}{100} \right).......2\] Dividing, \[\frac{600}{800}=\frac{1+\frac{6r}{100}}{1+\frac{10r}{100}}\] \[\Rightarrow \frac{6}{8}=\frac{3}{4}=\frac{1+\frac{6r}{100}}{1+\frac{10r}{100}}\] Cross multiplying, \[3+\frac{30r}{100}=4+\frac{24r}{100}\] \[\frac{6r}{100}=1\] \[r=\frac{100}{6}=16.66%\]

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