11th Class Mental Ability Numbers Question Bank Question - Number System

  • question_answer
    If \[\mathbf{a=}\frac{\mathbf{x}}{\mathbf{x+y}}\]and \[\mathbf{b=}\frac{\mathbf{y}}{\mathbf{x-y}}\], then \[\frac{\mathbf{ab}}{\mathbf{a+b}}\]is equal to:

    A) \[\frac{xy}{{{x}^{2}}+{{y}^{2}}}\]

    B) \[\frac{{{x}^{2}}+{{y}^{2}}}{xy}\]

    C) \[\frac{x}{x+y}\]

    D) \[{{\left( \frac{y}{x+y} \right)}^{2}}\]

    E) None of these

    Correct Answer: A

    Solution :

    Explanation Option (a) is correct. \[\frac{ab}{a+b}\frac{\frac{x}{(x+y)}\times \frac{y}{\left( x-y \right)}}{\frac{x}{\left( x+y \right)}+\frac{y}{\left( x-y \right)}}\] \[=\frac{xy}{{{x}^{2}}-xy+xy+{{y}^{2}}}=\frac{xy}{{{x}^{2}}+{{y}^{2}}}\]


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