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Railways R.R.C. (Patna) Solved Paper Held on 1st_Shift 23-11-2014

  • question_answer
    If the radius of a sphere is increased by 2 cm, it's surface area increases by\[352\,\,c{{m}^{2}}\].The radius of the sphere before change is?

    A) 7 cm                            

    B) 6 cm

    C) 5 cm                            

    D) 4 cm

    Correct Answer: B

    Solution :

    Suppose the radius of the sphere before charge is x. Then,    \[4\pi {{(x+2)}^{2}}-4\pi {{x}^{2}}=352\] \[4\pi [{{x}^{2}}+4+4x-{{x}^{2}}]=352\]             \[4x+4=\frac{352\times 7}{4\times 22}\]             \[4x+4=28\] \[4x=24\]                         \[x=6\,\,cm\]


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