Railways Sample Paper RRB (Assistant Loco Pilot) Sample Test Paper-1

  • question_answer
    The ussnit's digit in the product \[{{7}^{35}}\times {{3}^{71}}\times {{11}^{55}}\]is :

    A)  1                    

    B)         3                    

    C)         7                    

    D)         9

    Correct Answer: A

    Solution :

    Unit's digit in \[({{7}^{4}})=1.\]. Therefore, unit's digit in \[{{({{7}^{4}})}^{8}}\]i.e. \[{{7}^{32}}\]will be 1. Hence, unit's digit in  \[{{(7)}^{35}}=1\times 7\times 7\times 7=3\] Again, unit's digit in \[{{(3)}^{4}}=1\] Therefore, unit's digit in the expansion of \[{{({{3}^{4}})}^{17}}={{(3)}^{68}}=1\] \[\Rightarrow \]    Unit's digit in the expansion of \[({{3}^{71}})=1\times 3\times 3\times 3=7\] and unit's digit in the expanison of \[{{(11)}^{35}}=1\] Hence, unit's digit in the expansion of \[{{7}^{35}}\times {{3}^{71}}\times {{11}^{55}}=3\times 7\times 1=1\]


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