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Math Help - Probability?

  1. #1
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    Probability?

    Right, so I've got an upcoming exam tomorrow, and I just found out I'm stuck on probabilities (Not sure if that is what it's called in English).

    Anyways, the question goes like this :

    Troms skiing facility got 6 menn for NM in skiing. 2 of them are under the age of 20. It's a 4x7,5km lap, and they are going to pick 4 "runners(/skiiers)".

    a) What's the probablity for that NONE of the 2 under the age of 20 does this?
    b) What's the probablity for that minimum ONE of the 2 under the age of 20 does this?
    c) What's the probablity for that EXACTLY ONE of the 2 under the age of 20 does this?
    d)What's the probability that the skiier hit at least 4 of 5 targets with 5 shots.? (Hitting 1 target = 90%)

    If you could explain your answers, that would be great.
    I will most likely understand it, if you just set it up correctly.

    (Not even sure if I've been trying the right formula :
    X=x (n) p^x (1-p)^n-x
    ----(x) (<- not n divided by x)


    OR if you could do :

    Statistic over football matches in 2005 showed the probabilities for home victiory (H), tie (T), away victory (A).
    P(H) = 0,45, P(U) = 0,29, P(B)= 0,26

    a) What's the probability that ALL the twelve matches ends with home victory?
    b) How big is the posibility that the 6 first ends with home victory, and the next tree tie, and the last tree with away victory?
    c) Probability that there won't be an away victory?
    Last edited by Rawr; May 31st 2009 at 06:48 AM.
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  2. #2
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    Ok, on "c) Probability that there won't be an away victory?" I figured :
    P(H) = 0,45 + P(U) = 0,29 divided by 1.

    Does that add up?

    Also, I'm not sure how to approach these questions, could anyone give any kind of hints?

    Or a good explained answer?
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  3. #3
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    Quote Originally Posted by Rawr View Post
    Right, so I've got an upcoming exam tomorrow, and I just found out I'm stuck on probabilities (Not sure if that is what it's called in English).

    Anyways, the question goes like this :

    Troms skiing facility got 6 menn for NM in skiing. 2 of them are under the age of 20. It's a 4x7,5km lap, and they are going to pick 4 "runners(/skiiers)".

    a) What's the probablity for that NONE of the 2 under the age of 20 does this?
    b) What's the probablity for that minimum ONE of the 2 under the age of 20 does this?
    c) What's the probablity for that EXACTLY ONE of the 2 under the age of 20 does this?
    d)What's the probability that the skiier hit at least 4 of 5 targets with 5 shots.? (Hitting 1 target = 90%)

    If you could explain your answers, that would be great.
    I will most likely understand it, if you just set it up correctly.

    [snip]
    a) \frac{{2 \choose 0} \cdot {4 \choose 2}}{{6 \choose 2}}.


    b) \frac{{2 \choose 1} \cdot {4 \choose 1}}{{6 \choose 2}} + \frac{{2 \choose 2} \cdot {4 \choose 0}}{{6 \choose 2}} .


    c) \frac{{2 \choose 1} \cdot {4 \choose 1}}{{6 \choose 2}}.


    d) X ~ Binomial(n = 5, p = 0.9). Calculate \Pr(X \geq 4).

    Quote Originally Posted by Rawr View Post
    [snip]
    Statistic over football matches in 2005 showed the probabilities for home victiory (H), tie (T), away victory (A).
    P(H) = 0,45, P(U) = 0,29, P(B)= 0,26 Mr F says: What events do U and B represent?

    a) What's the probability that ALL the twelve matches ends with home victory?
    b) How big is the posibility that the 6 first ends with home victory, and the next tree tie, and the last tree with away victory?
    c) Probability that there won't be an away victory?
    a) (0,45)^12.
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  4. #4
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    Thank you mr. fantastic, even though it was a day late.

    I've already had my exam now .


    I did however find out how to do it in time.
    The formula I posted worked just fine, I think I accidentally wrote the wrong number or something when I tried it out.
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