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Math Help - Probability help

  1. #1
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    Probability help

    Hi im someone who is a strugglnig a little with the statistics part of his course! I have a couple of question and would be very grateful if someone could answer.
    I struggle a bit with turning equation into practical usage so if i see the working needed I will probably clock onto the concept very fast.


    'Information of a packet of seeds says the germination rate is 92%, what is the probability that 95% of seeds in the packet of 160 will germinate?'

    'The weight of a pakcet of crisps is 10 ounces, the amount that the packaging machene puts in these bags is beleived to have a normal model10.2 and a standard deviation 0.12 ounces
    a) what fraction of all bags sold are underweight
    b) what is the probablity that of a multipack fo 3 none are underweight
    c) what is the probability that the mean weight of the 3 bags is below the stated amount
    d) whats the probability that the mean weight of a 24 bag box of crisps is below 10 ounces
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  2. #2
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    Quote Originally Posted by AndrewFFC View Post
    Hi im someone who is a strugglnig a little with the statistics part of his course! I have a couple of question and would be very grateful if someone could answer.
    I struggle a bit with turning equation into practical usage so if i see the working needed I will probably clock onto the concept very fast.


    'Information of a packet of seeds says the germination rate is 92%, what is the probability that 95% of seeds in the packet of 160 will germinate?'

    [snip]
    Let X be the random variable number of seeds that germinate.

    X ~ Binomial(n = 160, p = 0.92)

    Calculate \Pr(X \geq 152).

    You could probably use the normal approximation to the binomial distribution to get the asnwer.
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  3. #3
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    Quote Originally Posted by AndrewFFC View Post
    [snip]

    'The weight of a pakcet of crisps is 10 ounces, the amount that the packaging machene puts in these bags is beleived to have a normal model10.2 and a standard deviation 0.12 ounces
    a) what fraction of all bags sold are underweight
    b) what is the probablity that of a multipack fo 3 none are underweight
    c) what is the probability that the mean weight of the 3 bags is below the stated amount
    d) whats the probability that the mean weight of a 24 bag box of crisps is below 10 ounces
    a) Calculate Pr(X < 10) = Pr(Z < 5/3) where the Z-value is found from Z = \frac{X - \mu}{\sigma}. I imagine you'll use either tables or technology.

    b) If the answer to a) is p, then the answer here is (1 - p)^3.

    c) The mean weight \overline{X} follows a normal distribution with \mu = 10.2 and \sigma = \frac{0.12}{\sqrt{3}}. Use this normal distribution to calculate \Pr(\overline{X} < 10).

    d) The mean weight \overline{X} follows a normal distribution with \mu = 10.2 and \sigma = \frac{0.12}{\sqrt{24}}. Use this normal distribution to calculate \Pr(\overline{X} < 10).
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