Results 1 to 2 of 2

Math Help - Problem (Geometric Progressions)

  1. #1
    Junior Member Lonehwolf's Avatar
    Joined
    Nov 2008
    Posts
    55

    Problem (Geometric Progressions)

    Records are kept of the number of copies of a certain book that are sold each week. In the first week after publication 3000 copies were sold, and in the second week, 2400 copies were sold. The publisher forecasts future sales by assuming that the number of copies sold each week will form a geometric progression with first two terms 3000 and 2400. Calculate the publisher's forecasts for

    (i) The number of copies that will be sold in the 20th week after publication.
    (ii) The total number of copies sold during the first 20 weeks after publication.
    (iii) The total number of copies that will ever be sold.
    Last edited by Lonehwolf; March 22nd 2009 at 07:14 AM. Reason: Solved
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Like a stone-audioslave ADARSH's Avatar
    Joined
    Aug 2008
    From
    India
    Posts
    726
    Thanks
    2
    Quote Originally Posted by Lonehwolf View Post
    Records are kept of the number of copies of a certain book that are sold each week. In the first week after publication 3000 copies were sold, and in the second week, 2400 copies were sold. The publisher forecasts future sales by assuming that the number of copies sold each week will form a geometric progression with first two terms 3000 and 2400. Calculate the publisher's forecasts for

    (i) The number of copies that will be sold in the 20th week after publication.
    (ii) The total number of copies sold during the first 20 weeks after publication.
    (iii) The total number of copies that will ever be sold.
    First term ,a = 3000

    Common ratio,

    r = \frac{2400}{3000} = \frac{4}{5}


    i) nth term of the sequence is given by

     <br />
T_n =a\times r^{n-1} <br />

     <br />
T_{20} =3000\times (\frac{4}{5})^{20-1} <br />

    ii) Sum upto nth term of GP is given by

    <br />
S_n = \frac{a(1-r^n)}{1-r} <br />

    Try putting the values yourself

    iii) Sum upto infinite terms of a GP with

    |r|< 1

    = \frac{a}{1-r}

    Put the values
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Arithmetic and Geometric Progressions
    Posted in the Algebra Forum
    Replies: 4
    Last Post: April 29th 2011, 01:06 AM
  2. Geometric Progressions
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: May 31st 2010, 06:06 PM
  3. Geometric Progressions
    Posted in the Algebra Forum
    Replies: 2
    Last Post: May 20th 2010, 01:28 PM
  4. geometric progressions
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: August 12th 2009, 03:10 PM
  5. Stuck on Geometric Progressions
    Posted in the Pre-Calculus Forum
    Replies: 7
    Last Post: January 22nd 2009, 03:10 AM

Search Tags


/mathhelpforum @mathhelpforum