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8th Class Mathematics Exponents and Power Question Bank Exponents and Powers

  • question_answer
    The value of \[{{({{7}^{-1}}-{{8}^{-1}})}^{-1}}-{{({{3}^{-1}}-{{4}^{-1}})}^{-1}}\] is

    A)  56                              

    B)  12      

    C)  68                  

    D)         44      

    Correct Answer: D

    Solution :

    We have, \[{{({{7}^{-1}}-{{8}^{-1}})}^{-1}}-{{({{3}^{-1}}-{{4}^{-1}})}^{-1}}\] \[={{\left( \frac{1}{7}-\frac{1}{8} \right)}^{-1}}-{{\left( \frac{1}{3}-\frac{1}{4} \right)}^{-1}}={{\left( \frac{8-7}{56} \right)}^{-1}}-{{\left( \frac{4-3}{12} \right)}^{-1}}\]\[={{\left( \frac{1}{56} \right)}^{-1}}-{{\left( \frac{1}{12} \right)}^{-1}}=56-12=44\]


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