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JEE Main & Advanced Mathematics Sequence & Series Question Bank Arithmetic Progression

  • question_answer
    If twice the 11th term of an A.P. is equal to 7 times of its 21st term, then its 25th term is equal to [J & K 2005]

    A) 24

    B) 120

    C) 0

    D) None of these

    Correct Answer: C

    Solution :

    Let the first term of A.P. is a and common difference is d. 11th term of A.P. = \[a+10d\] 21st term of A.P. = a+ 20d \[2(a+10d)=7(a+20d)\]Þ\[2a+20d=7a+140d\] \[5a+120d=0\]Þ\[a+24d=0\] Hence 25th term is 0.


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