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

  1. 10th
  2. 9th
  3. 8th
  4. None of these
Anurag Mishra Professor Asked on 12th October 2015 in Reasoning Questions.
Add Comment
  • 1 Answer(s)

    Answer: (2) 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 (2) 9th.

    Anurag Mishra Professor Answered on 12th October 2015.
    Add Comment
  • Your Answer

    By posting your answer, you agree to the privacy policy and terms of service.