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Math Help - Simple Probabilities Plz Help

  1. #1
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    Simple Probabilities Plz Help

    Hey,

    Can someone plz answer the following questions and provide explanation.

    1. P(E)=0.25 and 20 outcomes make up event E. Determine the number of outcomes?

    2. There are 7 girls, 9 boys in a school camera club. The club needs to form a committee of 6 random people. Determine the outcome if:
    a) The committee has no boys.
    b) The committee has at least 1 girl.

    3. You have a regular 6 side die. You roll it 2 times. Determine if:
    a) Probability that you roll a sum of 7.
    b) Probability that you roll a sum of 7 if the first roll is 5.

    Any help would be greatly appreciated.

    Thanx
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  2. #2
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    1. 20 \times 0.25 = 5 I'm not 100% sure about this one.

    2. so there are a total of 16 students and out of them you are interested in choosing six.

     \binom{16}{6} = 8008 possible picks.

    a)  P(X=0) = \frac{\binom{9}{0} \binom{7}{6}}{8008} = \frac{7}{8008}

    b)  P(Y \geq 1) = 1- P(Y=0) = 1- \frac{\binom{9}{6} \binom{7}{0}}{8008} = 1- \frac{84}{8008} = \frac{283}{286}

    3. your sample would consist of  S= (1,1), (1,2), ... , (6,6)

    a) so out of those there are 6 possible ways to get a 7 and 36= 6\times 6 outcomes. so you have:

     \frac{6}{36} = \frac{1}{6}

    b) P(7|5) = \frac{P(7 \cap 5)}{P(5)} =   \frac{1/36}{1/6} = \frac{1}{216}
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  3. #3
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    Thanx for the help llll and mathstud.
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  4. #4
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    shoudnt the answer for 3b) equal 1/6 not 1/216???
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  5. #5
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    I really wish that if you do not understand the process that you would reframe from giving totally wrong information.
    If P(E)=0.25 and 20 outcomes make up event E then clearly E happens in of the experiences, so there would have been 80 experiences.
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  6. #6
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    Quote Originally Posted by ballin_sensation View Post
    shoudnt the answer for 3b) equal 1/6 not 1/216???
    you are correct it should be 1/6, I made a mistake punching it in my calculator.
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