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NTSE Sample Paper NTSE MAT Practice Test-12

  • question_answer
      In the series 3,9, 15, ....., what will be the

    A)  117          

    B)  121

    C)  123

    D) 129

    Correct Answer: C

    Solution :

    3,9, 15,......21st term.           \[\Rightarrow 3\times 1,\text{ }3\times 3,\text{ }3\times 5,\text{ }....\text{ }3\text{ }\times \text{ }21st\] odd number.                                                                                                      \[\Rightarrow\]  21st term                                                                               \[=3\times \left( 2\times 21-1 \right)\]                                                                                         \[-3\times 41=\text{ }123.\] (Note nth odd number is                                                                                               \[\left( 2n-1 \right)).\]


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