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

  • question_answer
    A How many plants (approximately) will be there in a circular bed whose outer edge measures 30 cm allowing \[4\text{ }c{{m}^{2}}\]for each plant?

    A)  \[18\]      

    B)  \[750\]          

    C)  24                  

    D)  120

    Correct Answer: A

    Solution :

    (a): From data it is clear that 30 cm = perimeter \[=2\pi r\] \[\Rightarrow \,\,r=\frac{15}{\pi }\] \[\therefore \] Area \[=\pi {{r}^{2}}=\pi \times \frac{{{\left( 15 \right)}^{2}}}{{{\pi }^{2}}}\] \[=\frac{225}{\pi }\] No. of plant \[=\frac{Area}{Area\,\,per\,\,plant}=\frac{225/\pi }{4}=\frac{225}{4\pi }\approx 18\]                


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