8th Class Mathematics Mensuration Question Bank Mensuration

  • question_answer If the area of base of a cone is 154 cm2 and height is 9 cm, then the curved surface area of cone will be

    A)  200.53 \[c{{m}^{2}}\]            

    B)  220.53 \[c{{m}^{2}}\]      

    C)  240.8 \[c{{m}^{2}}\]                         

    D)  250.8 \[c{{m}^{2}}\]

    Correct Answer: D

    Solution :

    (d): \[\pi rl=\pi r\sqrt{{{r}^{2}}+{{h}^{2}}}\] \[\pi {{r}^{2}}=154={{\pi }^{2}}=\frac{154}{\pi }\,\,and\,\,r=\sqrt{\frac{154}{22/7}=7}\] \[\therefore \pi rl=\frac{22}{7}\times 7\times \sqrt{49+{{9}^{2}}}\] \[=22\times \sqrt{130}=250.8.\]

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