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7th Class Mathematics Mensuration Question Bank Mensuration (Perimeter & Area)

  • question_answer
    The length of a rectangular field is increased by 60% and its breadth is decreased by 40% to form a new rectangular field. Find the percentage change in the area of a the field.

    A)  20% measure

    B)  4% decrease   

    C)  20 % decrease           

    D)  4% increase

    Correct Answer: B

    Solution :

    (b): \[\left. \begin{align}   & 1\to 1\times \left( 1+\frac{60}{100} \right)=1.61 \\  & b\to b\times \left( 1-\frac{40}{100} \right)=0.6\,b \\ \end{align} \right\}\] old area \[=1\times b,\] new area \[=1.61\times 0.6\,b=(0.96)\,1b\] \[\therefore \] Percentage decrease \[=Ib-0.96\text{ }Ib=0.04=4%\]


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