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Math Help - probability with teen pregnancy

  1. #1
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    probability with teen pregnancy

    heres the question.
    What is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she is classified as white ? what is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she classified as black.

    heres the chart
    -----------------15 to 17 -----------------18 to 19
    white--------------23------------------------.49
    black--------------.09-----------------------.15
    other--------------.01-----------------------.03

    THANKSS!! any help would be helpful!
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  2. #2
    Bar0n janvdl's Avatar
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    Quote Originally Posted by gbgb View Post
    heres the question.
    What is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she is classified as white ? what is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she classified as black.

    heres the chart
    -----------------15 to 17 -----------------18 to 19
    white--------------23------------------------.49
    black--------------.09-----------------------.15
    other--------------.01-----------------------.03

    THANKSS!! any help would be helpful!
    Use Bayes' Rule.

    For white:

    P(15-17 | W) = \frac{P(W | 15-17)P(15-17)}{P(W | 15-17)P(15-17) + P(W | 18-19)P(18-19)}

    = \frac{(.23)(.33)}{(.23)(.33) + (.49)(.67)}

    For black:

    P(15-17 | B) = \frac{P(B | 15-17)P(15-17)}{P(B | 15-17)P(15-17) + P(B | 18-19)P(18-19)}

    = \frac{(.09)(.33)}{(.09)(.33) + (.15)(.67)}
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  3. #3
    Grand Panjandrum
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    Quote Originally Posted by gbgb View Post
    heres the question.
    What is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she is classified as white ?
    23/(23+49)~=0.319

    Explanation: in a sample of 100 teen pregnancies 72 are white, and of those 23 are "15 to 17"'s (on average)

    RonL
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