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Math Help - Probability help

  1. #1
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    Question Probability help

    Hi, I'm stuck with this, if anyone can help, it'll be awesome!

    1. Four-fifths of all volunteers working in a charity shop are over 50. If two volunteers are chosen at random, what is the probability that one of them is over 50, but the other one is not?


    • 0.04
    • 0.2
    • 0.16
    • 0.32
    • None of the above
    2. A producer of 'home-made' biscuits is known to produce biscuits whose thicknesses are Normally-distributed. If the mean thickness is 4mm with a standard deviation of 0.6mm, approximately what proportion of biscuits will be thicker than 5mm?


    • 0.9525
    • 0.0446
    • 0.0475
    • 0.4325
    • None of the above

    what is the quickest way or formula or working it out?
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  2. #2
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    Quote Originally Posted by chungkayan View Post
    Hi, I'm stuck with this, if anyone can help, it'll be awesome!

    1. Four-fifths of all volunteers working in a charity shop are over 50. If two volunteers are chosen at random, what is the probability that one of them is over 50, but the other one is not?


    • 0.04
    • 0.2
    • 0.16
    • 0.32
    • None of the above
    2. A producer of 'home-made' biscuits is known to produce biscuits whose thicknesses are Normally-distributed. If the mean thickness is 4mm with a standard deviation of 0.6mm, approximately what proportion of biscuits will be thicker than 5mm?


    • 0.9525
    • 0.0446
    • 0.0475
    • 0.4325
    • None of the above
    what is the quickest way or formula or working it out?
    1. Assuming a large population (so that it's essentially a sampling with replacement problem): X ~ Binomial(n = 2, p = 4/5). Calculate Pr(X = 1).

    2. Pr(X > 50) = Pr(Z > (5 - 4)/0.6) = Pr(Z > 5/3) = 1 - Pr(Z < 5/3).
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  3. #3
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    Sorry, call me slow. but i didn't really catch that. whats the formula for first one?
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  4. #4
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    Quote Originally Posted by chungkayan View Post
    Sorry, call me slow. but i didn't really catch that. whats the formula for first one?
    Have you studied the binomial distribution?
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  5. #5
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    No, I haven't is there a link to study it? many thanks
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  6. #6
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    Quote Originally Posted by chungkayan View Post
    No, I haven't is there a link to study it? many thanks
    Binomial distribution - Wikipedia, the free encyclopedia
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