10th Class Mathematics Pair of Linear Equations in Two Variables Question Bank MCQs - Pair of Linear Equations in Two Variables

  • question_answer
    Solve the pair of the equations: \[\frac{2}{x}+\frac{3}{y}=13,\] \[\frac{3}{x}+\frac{6}{y}=21\]

    A) \[x=\frac{2}{5},y=1\]

    B) \[x=\frac{1}{2},y=\frac{1}{3}\]

    C) \[x=\frac{1}{5},y=1\]

    D) \[x=\frac{2}{3},y=-3\]

    Correct Answer: C

    Solution :

    [c] The given system of equations is
    \[\frac{2}{x}+\frac{3}{y}=13\] and \[\frac{3}{x}+\frac{6}{y}=21\]
    Putting \[\frac{1}{x}=p\] and \[\frac{1}{y}=q,\] we get
    \[2p+3q=13\]                         ...(1)
    and     \[3p+6q=21\Rightarrow p+2q=7\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,p=7-2q\]                         ...(2)
    Substituting the value of p in eq. (1), we get
                \[2(7-2q)+3q=13\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,14-4q+3q=13\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,q=1\]
    Substituting \[q=1\] in eq. (2), we get
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,p=7-2(1)=5\]
    Now      \[\frac{1}{x}=5\Rightarrow x=\frac{1}{5}\] and \[\frac{1}{y}=1\Rightarrow y=1\]


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