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Homework Help: Kept getting the wrong answer? binomial conditional probability

  1. Nov 14, 2011 #1
    Product Testing A supposed coffee connoisseur claims she can distinguish between a cup of instant coffee and a cup of drip coffee 75% of the time. You give her 5 cups of coffee and tell her that you will grant her claim if she correctly identifies at least 4 of the 5 cups.

    (a) What are her chances of having her claim granted if she is in fact only guessing?

    i did
    C(5,4)* .75^4 *.25 get the exactly 4 add .75^5 to get exactly 5.
    i got 0.6328 but my online hw kept saying that it 's wrong.
  2. jcsd
  3. Nov 14, 2011 #2
    Hint: consider what would be the probability of success if she was testing a single cup and only guessing.

    Edit: this thread belongs in the homework forums
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