JEE Main & Advanced Sample Paper JEE Main - Mock Test - 4

  • question_answer
    The value of \[^{505}{{C}_{5}}-5.\] \[^{404}{{C}_{5}}+10.\] \[^{303}{{C}_{5}}-10.\]\[^{202}{{C}_{5}}+5.\]\[^{101}{{C}_{5}}\] is equal to                            

    A)  \[{{101}^{5}}\]          

    B) \[101\]                  

    C) \[{{201}^{5}}\]                

    D) \[^{201}{{C}_{5}}\]

    Correct Answer: A

    Solution :

    [a] \[^{505}{{C}_{5}}-5{{\times }^{404}}{{C}_{5}}+10{{\times }^{303}}{{C}_{5}}-10{{\times }^{202}}{{C}_{5}}+5{{\times }^{101}}{{C}_{5}}-1+1\]= coefficient of \[{{x}^{5}}\] in \[{{(1+x)}^{505}}-5{{(1+x)}^{404}}\] \[+10{{(1+x)}^{303}}-10{{(1+x)}^{202}}+5{{(1+x)}^{101}}-1+1\] = coefficient of \[{{x}^{5}}\] in  \[{{[{{(1+x)}^{101}}-1]}^{5}}+1\] \[={{{{(}^{101}}{{C}_{1}})}^{5}}\]


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