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9th Class Mathematics Areas of Parallelograms and Triangles Question Bank Area of Parallelogram & Triangle

  • question_answer
    The length of a room floor exceeds its breadth by 20 m. The area of the floor remains unaltered when the length is decreased by 10 m but the breadth is increased by 5 m. The area of the floor (in square metres) is

    A)  280                           

    B)  325

    C)  300   

    D)  420

    Correct Answer: C

    Solution :

    (c): Let the breadth of floor be \[x\] metre. \[\therefore \]Length \[=\left( x+20 \right)\] metre \[\therefore \]Area of the floor \[\left( x+20 \right)x\] sq. metre According to question, \[\left( x+10 \right)\left( x+5 \right)=x\left( x+20 \right)\] \[\Rightarrow \]\[{{x}^{2}}+15x+50={{x}^{2}}+20x\] \[\Rightarrow \]\[20x=15x+50\] \[\Rightarrow \]\[5x=50\] \[\Rightarrow \]\[x=10\] metre \[\therefore \]Length \[=x+20=10+20=30\] metre \[\therefore \]Area of the floor \[=30\times 10=300\] sq. metre                                 


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