7th Class Mental Ability Related to Competitive Exam Question Bank Mensuration

  • question_answer
    A wire, when bent in the form of a square, encloses an area of \[\mathbf{484}\text{ }\mathbf{c}{{\mathbf{m}}^{\mathbf{2}}}\]. If the same wire is bent in the form of a circle then find the area enclosed by it.

    A) \[161\text{ }c{{m}^{2}}\]                   

    B) \[166\text{ }c{{m}^{2}}\]

    C) \[\text{616 }c{{m}^{2}}\]  

    D) \[\text{916 }c{{m}^{2}}\]

    E) None of these

    Correct Answer: C

    Solution :

    Explanation \[\operatorname{Area} of square = 484 c{{m}^{2}}\] \[\operatorname{Side}\,\,of\,\,square=\,\,\sqrt{484}\,\,=\,\,22cm\] \[\operatorname{Perimetre} of square = 4 \times  22 cm = 88 cm\] Let r be the radius of the circle. Same wire is bent in the form of a square and circle. Therefore, circumference of the circle = perimetre of the square. or \[2\pi r = 88\] \[2\times \frac{22}{7} \times  r = 88 \,\Rightarrow  \,r = \frac{88\times 7}{2\times 22} = 14 cm\] Thus area of circle \[= \,\pi {{r}^{2}}\,\,=\,\,\frac{22}{7} \times  14 \times  14 = 616 c{{m}^{2}}.\]      


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