Railways Quantitative Aptitude Number System and its Operations Sample Paper Number System Sample Test Paper-1

  • question_answer
    The unit'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 :

    [a]   Units digit in \[({{7}^{4}})=1.\] Therefore, units digit in\[{{({{7}^{4}})}^{8}}\] i.e. \[{{7}^{32}}\] Will be 1. Hence, units 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 units digit in the expansion of \[({{11}^{35}})=1\] Hence, units digit in the expansion of \[{{7}^{35}}\times {{3}^{71}}\times {{11}^{55}}=3\times 7\times 1=1\]


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