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Railways R.R.C. (Delhi) Solved Paper Held on 1st Shift 2-11-2014

  • question_answer
    If\[1+x+{{x}^{2}}+{{x}^{3}}=60\], then the average of \[x,\,\,{{x}^{2}},\,\,{{x}^{3}}\,\,and\,\,{{x}^{4}}\]is equal to which of the following?

    A) \[30x\]                          

    B) \[12x\]

    C) (c)\[15x\]                                  

    D) \[20x\]

    Correct Answer: C

    Solution :

    Given, \[1+x+{{x}^{2}}+{{x}^{3}}=60\] then, \[\frac{x+{{x}^{2}}+{{x}^{3}}+{{x}^{4}}}{4}=\frac{x\,\,(1+x+{{x}^{2}}+{{x}^{3}})}{4}\] \[=\frac{60x}{4}=15x\]


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