JEE Main & Advanced Mathematics Sets Question Bank Critical Thinking

  • question_answer If \[{{N}_{a}}=\{an:n\in N\},\] then \[{{N}_{3}}\cap {{N}_{4}}=\]

    A) \[{{N}_{7}}\]

    B) \[{{N}_{12}}\]

    C) \[{{N}_{3}}\]

    D) \[{{N}_{4}}\]

    Correct Answer: B

    Solution :

    \[{{N}_{3}}\cap {{N}_{4}}=\{3,\,6,\,9,\,12,15......\}\cap \{4,\,8,\,12,\,16,\,20,.....\}\]    = {12, 24, 36......} = \[{{N}_{12}}\]. Trick: \[{{N}_{3}}\cap {{N}_{4}}={{N}_{12}}\] [\[\because \] 3, 4 are relatively prime numbers].


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