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Calculate the sum of the infinite series 72 + 60 + 50 + 125/3 + ...

489
432
360
307

Can someone please help me with this one? I can never solve these on my own:(

  • Math -

    if it is geometric, r=60/72=10/12=5/6
    adn then 5/6(60=50
    and then 40(5/6)=200/6=100/3, so that is not a geometric series. Did your teacher make an error? Lets test if she meant it to be a geometric series, r=5/6

    sum=72/(1-5/6)=72*6=amazing, the answer is there.

    So I bet your teacher meant 100/3 as the fourth term.

  • Math -

    Oh ok, thank you so much.

  • Math -

    Nah. Where did you get the 40? 50 * 5/6 = 250/6 = 125/3

    so, you have a genuine GP, with
    a = 72
    r = 5/6

    So, S = 72/(1 - 5/6) = 72*6 = 432

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