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Homework Help: Simple Probability Question

  1. Sep 27, 2010 #1
    Should be simple enough... unfortunately I'm 20 years removed from college and can't seem to find an equation so I thought I'd post it here.

    If there is a 30% chance that Bob will give me a $1, and a 30% chance that Ted will give me a $1 and a 30% chance that Frank will give me a $1. What are the chances that at least one of them gives me a $1?

    Very hypothetical, but if someone could give me the equation to solve it then I can figure some other problems out on my own.

  2. jcsd
  3. Sep 27, 2010 #2


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    The chance that at least one will give you a dollar is 100% minus the chance that none will give you a dollar. The chance that none will give you a dollar is the chance that the first won't give you a dollar times the chance the second won't times the chance the third won't.
  4. Sep 27, 2010 #3
    So... if I get this straight

    1 - (.7 x .7 x .7) = 65.7% ???
  5. Sep 27, 2010 #4


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    Yup, or you can look at all the combinations that can occur, e.g. Bob gives you a dollar and Ted and Frank don't, and so on, and then sum the appropriate probabilities.
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