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9th Class Mathematics Number System and its Operations Question Bank Number System

  • question_answer
    If\[{{\mathbf{2}}^{\mathbf{x-1}}}\mathbf{+}{{\mathbf{2}}^{\mathbf{x+1}}}\mathbf{=640}\], the value of x is

    A)  7                    

    B)  8     

    C)  9                                

    D)  6

    Correct Answer: B

    Solution :

    (b): \[{{2}^{x-1}}\left[ 1+{{2}^{2}} \right]=640\] \[{{2}^{x-1}}=128={{2}^{7}}\,\,\,\Rightarrow x-1=7,x=8\]       


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