10th Class Mathematics Mensuration Question Bank Mensuration

  • question_answer
    A cone whose height is 15 cm and radius of base is 6 cm, is trimmed sufficiently to reduce it to a pyramid whose base is an equilateral triangle. The volume of the portion of removed is

    A) \[\text{325 c}{{\text{m}}^{\text{3}}}\]           

    B)         \[\text{328 c}{{\text{m}}^{\text{3}}}\]

    C) \[\text{33}0\text{ c}{{\text{m}}^{\text{3}}}\]           

    D)         \[\text{332 c}{{\text{m}}^{\text{3}}}\]  

    Correct Answer: D

    Solution :

     Height of cone \[=15\text{ }cm,\]Radius of cone \[=6\text{ m}\] \[\therefore \]Volume of cone \[=\frac{1}{3}\pi \,\,{{r}^{2}}h\]                 \[=\frac{1}{3}\times \frac{22}{7}\times 6\times 6\times 15\]                 \[=\frac{3960}{7}\,cu.\,cm.\]                 \[=565.71\,cu.\,cm\] Now base of the pyramid is an equilateral triangle of side \[6\text{ }cm\] \[\therefore \]  Area of equilateral triangle                 \[=\frac{\sqrt{3}}{4}\times {{(6\sqrt{3})}^{2}}=27\sqrt{3}\] \[\therefore \] Volume of pyramid of height \[15\text{ }cm\]                 \[=\frac{1}{3}\times 27\sqrt{3}\times 15\]                 \[=135\sqrt{3}\]                 \[=233.82\] Hence, difference of volume of cone and pyramid                 \[=(565.71-233.82\]                 \[=332\,cu.\,cm\,\,(app.)\]


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