Normal distribution question? URGENT!!

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  1. Cinnamon_Twist's Avatar
    1 17-05-2012  21:42
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    Normal distribution question? URGENT!!
    X-N (45, SIGMA)
    P(W<54)=0.75
    SO 54-45/SIGMA = 0.67
    I don't understand where the 0.67 has come from, it's not in any of the tables what happened to the 0.75, why is it 0.67
    This came up in a paper before but I didn't understand it :'(
    This question was from June 2007 Edexcel S1 Q2e
    Please help me someone, my exam is tomorrow!
    Thanks
  2. Cinnamon_Twist's Avatar
    2 17-05-2012  22:15
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    Re: Normal distribution question? URGENT!!
    BUMP
  3. Cinnamon_Twist's Avatar
    3 17-05-2012  22:16
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    Re: Normal distribution question? URGENT!!
    Sorry for the bumping but this is really urgent
  4. Cinnamon_Twist's Avatar
    4 17-05-2012  22:16
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    • Location: London
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    Re: Normal distribution question? URGENT!!
    (Original post by Cinnamon_Twist)
    X-N (45, SIGMA)
    P(W<54)=0.75
    SO 54-45/SIGMA = 0.67
    I don't understand where the 0.67 has come from, it's not in any of the tables what happened to the 0.75, why is it 0.67
    This came up in a paper before but I didn't understand it :'(
    This question was from June 2007 Edexcel S1 Q2e
    Please help me someone, my exam is tomorrow!
    Thanks
    just so I can find it easily
  5. Implication's Avatar
    5 17-05-2012  22:17
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    Re: Normal distribution question? URGENT!!
    P(W&lt;54)=0.75


    P(Z&lt;\frac{54-45}{\sigma})=0.75

    Reading \ backwards \ from \ the \ tables, \ P(Z&lt;0.67) \approx 0.75

    \therefore \ P(Z&lt;\frac{54-45}{\sigma}) \approx P(Z&lt;0.67) \ i.e. \ \frac{54-45}{\sigma} \approx 0.67
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  6. olipal's Avatar
    6 17-05-2012  22:22
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    • Location: London
    Re: Normal distribution question? URGENT!!
    I think you may be over-complicating things. Doesn't the question just ask you to find \sigma? You've done most of the work already!
    Post rating:
    1
  7. Cinnamon_Twist's Avatar
    7 17-05-2012  22:36
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    Re: Normal distribution question? URGENT!!
    (Original post by Implication)
    P(W&lt;54)=0.75


    P(Z&lt;\frac{54-45}{\sigma})=0.75

    Reading \ backwards \ from \ the \ tables, \ P(Z&lt;0.67) \approx 0.75

    \therefore \ P(Z&lt;\frac{54-45}{\sigma}) \approx P(Z&lt;0.67) \ i.e. \ \frac{54-45}{\sigma} \approx 0.67
    Thank you so so so so much! +rep

    (Original post by olipal)
    I think you may be over-complicating things. Doesn't the question just ask you to find \sigma? You've done most of the work already!
    yeah, I think I just panicked because the exam is tomorrow- thanks for the reassurance!
    +rep
  8. myme's Avatar
    8 17-05-2012  22:38
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    Re: Normal distribution question? URGENT!!
    umm.. >>>http://www.examsolutions.co.uk/a-lev...d-solution.php <<< check it! =) hope it would help.
  9. Rossshaw's Avatar
    9 23-05-2012  12:42
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    Re: Normal distribution question? URGENT!!
    (Original post by olipal)
    I think you may be over-complicating things. Doesn't the question just ask you to find \sigma? You've done most of the work already!
    Maths, Palmer Maths
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