10th Class Mathematics Areas Related to Circles Question Bank MCQs - Areas Related to Circles

  • question_answer
    If the perimeter of a circle is equal to that of a square, then the ratio of their areas is:    (NCERT exemplar)

    A) \[22:7\]

    B) \[14:11\]

    C) \[7:22\]

    D) \[11:14\]

    Correct Answer: B

    Solution :

    [b] Let radius of a circle be r and side of a square be a.
    Perimeter of a circle = Perimeter of a square   
    \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,\,2\pi r=4a\,\,\,\Rightarrow \,\,\,a=\frac{\pi r}{2}\]...(1)    
    Now, \[\frac{\text{Area of a circle}}{\text{Area of a square}}=\frac{\pi {{r}^{2}}}{{{(a)}^{2}}}=\frac{\pi {{r}^{2}}}{{{\left( \frac{\pi r}{2} \right)}^{2}}}\]
    [From eq.(1)]
    \[=\frac{\pi {{r}^{2}}}{{{\pi }^{2}}{{r}^{2}}/4}=\frac{4}{\pi }=\frac{4}{22/7}=\frac{28}{22}=\frac{14}{11}\]
    \[\therefore \]  Required ratio \[=14:11\]


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