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Probability question?

  1. Feb 13, 2012 #1
    1. The problem statement, all variables and given/known data

    This is one of my study guide questions and I need a little help

    Suppose that in a class of 500 students 210 smoke, 258 drink, 216 snack, 122 smoke and drink, 83 snack and drink, 97 smoke and snack, and 52 do all three. What is the probability that a student:
    (a) smokes but doesn't not drink
    (b) snacks and drinks, but doesn't smoke
    (c) neither smokes or drinks


    2. Relevant equations



    3. The attempt at a solution

    Sm=smokes
    D=drinks
    Sn=snacks

    (a) Prob(Sm [itex]\cap[/itex] ~D) = P(Sm)-P(Sm[itex]\cap[/itex]D = (210/500)-??
     
  2. jcsd
  3. Feb 13, 2012 #2

    lanedance

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    have you tried drawing a venn diagram?
     
  4. Feb 13, 2012 #3
    yes, but i'm getting confused because of the probability part
     
  5. Feb 13, 2012 #4

    lanedance

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    the probabilty of any portion of the venn diagram is just the number of students in it divided by 500
     
  6. Feb 13, 2012 #5
    this is my diagram... but how many people are left in c? i feel like this problem is simple but i'm just not seeing it
     

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  7. Feb 13, 2012 #6

    lanedance

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    you should have 3 circles, start filling it form the middle out

    you know 52 do all three

    and you know 97 smoke and snack

    this mean 97-52=45 smoke and snack but do not drink, and so on
     
  8. Feb 13, 2012 #7
    wow! it says it right in the question..nevermind lol
     
  9. Feb 13, 2012 #8
    thank you for your help!
     
  10. Feb 14, 2012 #9
    [itex]\cup[/itex]
     
  11. Feb 14, 2012 #10

    lanedance

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    no worries
     
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