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Series and sequences

  1. Jun 27, 2010 #1
    I don't understand anything about this question:

    In a pest eradication program, N sterilized male flies are released into the general population each day, and 90% of these flies will survive a given day.
    A) Show that the number of sterilized flies in the population after n days is
    N + (.9)N + (.9)2N + ...... + (.9)n-1N​

    B) If the long ranger goal (infinite) of the program is to keep 20,000 sterilized males in the population, how many such flies should be released each day?​
  2. jcsd
  3. Jun 27, 2010 #2


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    Science Advisor

    What is your question? What have you done on this and where did you have problems?
  4. Jun 27, 2010 #3
    Try to build a series that simulates the expression in your problem !
    May be try a geometric series, its easy to work with and the big plus is that you know the sum of this series.
  5. Jun 27, 2010 #4


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    Homework Helper

    Let's look at the first few terms.

    At the start of the first day there are N flies, that the end of the first day there are [tex]0.1N[/tex] flies left.

    At the start of the second day there will be 0.1N+N=1.1N flies. At the end of the second day there will be 10% of these left = 0.1*(1.1N)=0.11N flies.

    At the start of the third day there will be 0.11N+N=1.11N flies. At the end of the third day there will be 10% of these left = 0.1*(1.11N)=0.111N flies.

    Can you see where this is going? This is a geometric series.
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