Which is the Term of 1280 in Series 5, 10, 20, 40, ……………?

  1. 7th
  2. 10th
  3. 9th
  4. None of these

 

 

Anurag Mishra Professor Asked on 18th April 2016 in Maths.
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  • 1 Answer(s)

    Answer: (3) 9th

    Explanation:-
    5, 10, 20, 40, ……………………
    Then, 5 x 2 = 10,    10 x 2 = 20,      20 x 2 = 40 …………….

    Then, a = 5  and r = 2
    Therefore, the given series is G. P. (Geometric Progression),
    Let the number of terms be n.
    Then, 5 x 2n – 1 = 1280
    2n – 1 = 1280/5
    2n – 1 = 256
    2n – 1 = 28
    n – 1 = 8
    n  = 8 + 1
    n = 9

    Then, the 9th term is 1280.

    Hence, the answer is (3) 9th.

    Anurag Mishra Professor Answered on 23rd April 2016.
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