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Homework Help: Probability of soft-drink machine

  1. Feb 24, 2009 #1
    A soft-drink machine discharges an average of 200 ml per cup, with a standard deviation of 15 ml. What is the probability that a cup contains between 191 and 209 ml?


    Attempt:

    [tex]Z_1 = \frac{190.5-200}{15} = -0.63[/tex]

    [tex]Z_2 = \frac{209.5-200}{15} = 0.63[/tex]

    The table in my book "Areas under the normal curve", gives P = 0.7357-0.2643 = 0.4714

    Correct answer (according to the same book): 0.4514

    Are my continuity corrections wrong?
     
  2. jcsd
  3. Feb 25, 2009 #2
    I don't think that you need a continuity correction here, unless the problem specifies that the machine can only dispense discrete amounts.

    (209 - 200)/15 = .6

    P(Z < .6) = .7257
    .7257 - (1-.7257) = .4514
     
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