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Math Help - find expected value, standard deviation, and probability

  1. #1
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    find expected value, standard deviation, and probability

    this is a homework help. I'm stumped as to which formula or chapter to look at. please show guidance. IM NOT ASKING FOR AN ANSWER, just guidance.

    Q4. In a Gallup poll, 47% of the eligible women responding said that they would date a coworker. Suppose 350 employed women were selected at random.
    a) What would be the expected value and standard deviation of the number of these women who would date a coworker?
    b) What is the probability that at least 180 of them would date a coworker?

    a) u = n*p = 380*0.47 = 178.6
    s = square root ( n*p*q) = square root ( 380*0.47*0.53) = 9.7232

    b) the "at least" is throwing me off. I have no idea how to start this.
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  2. #2
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    If I have 10 pizzas and I eat "at least" 7 of them it means I have eaten 7, 8, 9 or 10 of them.

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  3. #3
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    Quote Originally Posted by jd254 View Post
    this is a homework help. I'm stumped as to which formula or chapter to look at. please show guidance. IM NOT ASKING FOR AN ANSWER, just guidance.

    Q4. In a Gallup poll, 47% of the eligible women responding said that they would date a coworker. Suppose 350 employed women were selected at random.
    a) What would be the expected value and standard deviation of the number of these women who would date a coworker?
    b) What is the probability that at least 180 of them would date a coworker?

    a) u = n*p = 380*0.47 = 178.6
    s = square root ( n*p*q) = square root ( 380*0.47*0.53) = 9.7232

    b) the "at least" is throwing me off. I have no idea how to start this.
    Calculate \Pr(X \geq 180).
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  4. #4
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    do i use 180.5 due to correction for continuity?
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  5. #5
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    Quote Originally Posted by jd254 View Post
    do i use 180.5 due to correction for continuity?
    No. Read this: Stats: Normal Approximation to Binomial
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