Results 1 to 8 of 8

Math Help - Please Help

  1. #1
    Junior Member VDestinV's Avatar
    Joined
    May 2008
    Posts
    25

    Question Please Help

    I posted a question last night but all that happened was I became even more confused.

    The homework question is:

    Find the sum of each geometric series.
    a) S10 in the series $2500 + $2562.50 + $2626.56 + ...


    now i would normally use the formula

    tn= ar^n-1 except I do not know what tn equals. To find the ^n I need to know what tn is. Now can some one please help me.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,547
    Thanks
    539
    Hello, VDestinV!

    Find the sum of the geometric series.

    a) S_{10} in the series: . \$2500 + \$2562.50 + \$2626.56 + \hdots
    First, find the common ratio r.


    We have: . \frac{2562.50}{2500} \:=\:1.025

    . . . .and: . \frac{2626.56}{2562.50} \:=\:1.024999024

    The common ratio appears to be: . r \:=\:1.025


    Then: . S_{10} \;=\;2500\,\frac{1.1025^{10}-1}{1.025-1} \;=\;128,008.4544 \:\approx\:\$128,008.45

    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member VDestinV's Avatar
    Joined
    May 2008
    Posts
    25
    Quote Originally Posted by Soroban View Post
    Hello, VDestinV!

    First, find the common ratio r.


    We have: . \frac{2562.50}{2500} \:=\:1.025

    . . . .and: . \frac{2626.56}{2562.50} \:=\:1.024999024

    The common ratio appears to be: . r \:=\:1.025


    Then: . S_{10} \;=\;2500\,\frac{1.1025^{10}-1}{1.025-1} \;=\;128,008.4544 \:\approx\:\$128,008.45
    wow thanks... but uhh what about the n?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member
    Joined
    May 2008
    Posts
    186
    10 is n, as I explained in the other thread.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member VDestinV's Avatar
    Joined
    May 2008
    Posts
    25
    Quote Originally Posted by Soroban View Post
    Hello, VDestinV!

    First, find the common ratio r.


    We have: . \frac{2562.50}{2500} \:=\:1.025

    . . . .and: . \frac{2626.56}{2562.50} \:=\:1.024999024

    The common ratio appears to be: . r \:=\:1.025


    Then: . S_{10} \;=\;2500\,\frac{1.1025^{10}-1}{1.025-1} \;=\;128,008.4544 \:\approx\:\$128,008.45
    I was looking over your calculations...

    shouldn't . S_{10} \;=\;2500\,\frac{1.1025^{10}-1}{1.025-1} \;=\;128,008.4544 \:\approx\:\$128,008.45

    actually be . S_{10} \;=\;2500\,\frac{1.025^{10}-1}{1.025-1} \;=\;28,008.4544 \:\approx\:\$28,008.45
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Member
    Joined
    May 2008
    Posts
    186
    Yes, that's correct.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member VDestinV's Avatar
    Joined
    May 2008
    Posts
    25
    okay but i tried to do that with this one but it didnt work

    s12 in the series 60, 12, 2.4, ...
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Member
    Joined
    May 2008
    Posts
    186
    Quote Originally Posted by VDestinV View Post
    okay but i tried to do that with this one but it didnt work

    s12 in the series 60, 12, 2.4, ...
    a = 60

    r = \frac{12}{60} = 0.2

    n = 12

    S_{12} = \frac{60(1 - 0.2^{12})}{1 - 0.2}

    S_{12} = 75
    Follow Math Help Forum on Facebook and Google+


/mathhelpforum @mathhelpforum