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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 28

  • question_answer
    Let \[X=\{1,\,\,2,\,\,3,\,\,4,\,\,5\}.\] Number of bijective mappings \[f:X\to X\] such that \[f(1)=1\] and \[f(2)\ne 2\] is                        

    A) \[12\]       

    B)                    \[15\]                   

    C) \[18\]              

    D)        \[36\]

    Correct Answer: C

    Solution :

      [c] \[f(1)=1\] For 2, there will be 3 cases. For 3, there will be 3 cases. For 4, there will be 2 cases. For 5, there will be 1 cases. \[\therefore \] Number of bijective functions \[=3\times 3\times 2\times 1=18\]  


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