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Homework Help: Pls help check my answer for this probability question.

  1. Aug 11, 2004 #1
    the lifespan of a species of plant is a random variable T ( tens of days ). the probability density function is given by

    f(t) = { (1/8)e^(-t/8) , t > 0
    { 0, otherwise

    (i) find the cumulative distribution function of T and sketch its graph

    i get this answer

    F(t) = { 0, t < or = 0
    { 1 - e^(-t/8) , t > 0

    (ii) find the probability, to three decimal places, that a plant of that species randomly chosen has a lifespan of more than 20 days

    i do it this way..

    F(2) = .....
    = 0.221

    P(lifespan > 20 days) = 1 - 0.221 = 0.779

    (iii) calculate the expected lifespan of that species of plant
    i get E(t) = 8
    therefore, expected lifespan of that species is 80 days.

    please tell me if i am correct in the questions above. sorry, i tried to use Latex but my attemp failed.
  2. jcsd
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