Results 1 to 2 of 2

Math Help - arithmetic progression--ans to confirm

  1. #1
    Member
    Joined
    Mar 2008
    Posts
    204

    arithmetic progression--ans to confirm

    Given :
    sequence of 5,7,9,11....

    Find :
    how many consecutive terms need to be added to obtain 357?

    My ans:
    n = 17 or -21(ignore)

    so n = 17

    tq for your time on it
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Mathstud28's Avatar
    Joined
    Mar 2008
    From
    Pennsylvania
    Posts
    3,641
    Quote Originally Posted by nikk View Post
    Given :

    sequence of 5,7,9,11....

    Find :
    how many consecutive terms need to be added to obtain 357?

    My ans:
    n = 17 or -21(ignore)

    so n = 17

    tq for your time on it
    So a_n=2(n+1)+1=2n+3

    So we must solve \sum_{n=1}^{k}\left\{2n+3\right\}=357

    Using the fact that \sum_{n=1}^{k} c=ck and \sum_{n=1}^{k}n=\frac{k(k+1)}{2} we must solve 2\cdot\frac{k(k+1)}{2}+3k=357. Solving indeed shows that the only pertinent answer is k=17

    Good job!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Arithmetic Progression
    Posted in the Algebra Forum
    Replies: 3
    Last Post: January 12th 2011, 10:40 AM
  2. Geometric Progression- Ans to confirm only
    Posted in the Algebra Forum
    Replies: 2
    Last Post: February 27th 2010, 08:40 PM
  3. Arithmetic Progression or Arithmetic Series Problem
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: October 8th 2009, 01:36 AM
  4. Replies: 8
    Last Post: March 23rd 2009, 08:26 AM
  5. Arithmetic progression
    Posted in the Algebra Forum
    Replies: 2
    Last Post: August 13th 2008, 08:33 AM

Search Tags


/mathhelpforum @mathhelpforum