7th Class Mathematics Mensuration Question Bank Mensuration

  • question_answer
    The length a rectangle is increased by 60%. By what percentage would the width have to be decreased to maintain the same area

    A)  \[37\frac{1}{2}%\]               

    B)  \[60%\]

    C)  \[75%\]                                  

    D)  \[120%\]

    Correct Answer: A

    Solution :

        Let the initial length and width are \[l\] and b respectively. Final length\[=l\times \frac{160}{100}\] Final width\[={{b}_{1}}\](say) Initial area = final area \[l\times b=l\times \frac{160}{100}\times {{b}_{1}}\Rightarrow {{b}_{1}}=\frac{100}{160}=\frac{5}{8}b\] Percentage decrement in width \[=\frac{b-{{b}_{1}}}{{{b}_{1}}}\times 100=\frac{b-\frac{5}{8}b}{b}\times 100%\] \[=37.5%\]     


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