CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2008

  • question_answer
    The remainder when \[{{3}^{100}}\times {{2}^{50}}\]is divided by 5 is

    A)  \[1\]                                    

    B)  \[2\]

    C)  \[3\]                                    

    D)  \[4\]

    Correct Answer: D

    Solution :

    Now,             \[{{3}^{2}}\equiv 4\,\,(\bmod \,5)\] \[\Rightarrow \]   \[{{({{3}^{2}})}^{2}}\equiv 16\,(\bmod \,5)\equiv 1\,(\bmod 5)\] \[\Rightarrow \]   \[{{({{3}^{4}})}^{25}}\equiv {{(1)}^{25}}(\bmod 5)\] \[\Rightarrow \]    \[{{3}^{100}}\equiv 1\,(\bmod 5)\] and \[{{2}^{2}}\equiv (\bmod \,5)\] \[\Rightarrow \]  \[{{({{2}^{2}})}^{2}}\equiv 16(\bmod \,5)\equiv 1(\bmod \,5)\] \[\Rightarrow \] \[{{({{2}^{4}})}^{12}}\equiv {{1}^{12}}(\bmod \,5)\equiv 1(\bmod \,5)\] \[\Rightarrow \] \[{{2}^{48}}{{.2}^{2}}\equiv 4(\bmod 5)\] \[\therefore \] \[{{3}^{100}}\times {{2}^{50}}=1\times 4(\bmod 5)\]      Hence, remainder is 4.


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