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Math Help - tree diagrams

  1. #1
    Super Member
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    Oct 2008
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    Bristol, England
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    tree diagrams

    Hi, This is my question:
    The prob of 20 year 9 students to have a swimming pool is 0.2.
    If they have a swimming pool the prob that they swim is 0.7.
    Draw a tree diagram.
    Find the prob of the year that swim.

    would i do this?

    tree diagrams-aaaa.jpg

    then would i do 0.7 X 0.3= 0.21?

    would this be corrects? if not where am i going wrong?
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  2. #2
    Newbie
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    Apr 2010
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    Bristol, England
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    Quote Originally Posted by andyboy179 View Post
    Hi, This is my question:
    The prob of 20 year 9 students to have a swimming pool is 0.2.
    If they have a swimming pool the prob that they swim is 0.7.
    Draw a tree diagram.
    Find the prob of the year that swim.

    would i do this?

    Click image for larger version. 

Name:	aaaa.jpg 
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ID:	16932

    then would i do 0.7 X 0.3= 0.21?

    would this be corrects? if not where am i going wrong?
    Prob of swimming with a pool + Prob of swimming without = Total Probability.

    Ie; (0.2*0.7) + (0.8*0.3) = .14 + .24 = .38 Therefore there is a 0.38 probability or 38 percent of year 9 will swim.
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  3. #3
    Super Member
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    Oct 2008
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    Bristol, England
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    897
    so on drawing the tree diagram on the no pool bit it would be, no pool - swim 0.3 and no swim 0.7?
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