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Approximate the Prob. in a normal distribution of a binomial

  1. Mar 22, 2012 #1
    1. The problem statement, all variables and given/known data
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    2. Relevant equations

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    3. The attempt at a solution
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  2. jcsd
  3. Mar 22, 2012 #2
    See, i was having trouble determining when to use the Continuity Correction in the problems, and i guess i still am. but i was able to match my answer with the given one from the back of the book when I stopped using it. however, the second problem doesn't match, even after using the new formula and the new percentage.

    I got .3264 and they got .3974

    Where am i going wrong here? anyone?
     
  4. Mar 22, 2012 #3

    Ray Vickson

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    You should NOT use the continuity correction in (a), because you are NOT approximating a discrete distribution by a continuous one; you are evaluating a probability for a truly continuous random variable. So, you get a slightly wrong probability in (a), then you use that incorrect value in (b).

    I get values different from yours and (presumably) from the book's. For (b) I get: exact probability = 0.374928, normal approx with continuity correction = 0.396911, normal approx without continuity correction = 0.472994.

    RGV
     
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