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Math Help - distribution

  1. #1
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    distribution

    Thank for all the help on the previous subject, now got one on distribution..

    In an examination it is known that the distribution of marks is N (52,24)

    a) what proportion of the marks will exceed 55?
    b) what proportion of the marks will be less than 45?

    c) if a grade A is awarded for the to p5% of marks, what is the minimum mark required in order to achieve a grade A?
    d) the bottom 20% of the marks was graded as an F, What was the range of these marks?

    Sorry for all the questions, had hundreds of these and stuck on a few of them
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  2. #2
    Junior Member F.A.P's Avatar
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    Quote Originally Posted by jimmybob View Post
    Thank for all the help on the previous subject, now got one on distribution..

    In an examination it is known that the distribution of marks is N (52,24)

    a) what proportion of the marks will exceed 55?
    b) what proportion of the marks will be less than 45?

    c) if a grade A is awarded for the to p5% of marks, what is the minimum mark required in order to achieve a grade A?
    d) the bottom 20% of the marks was graded as an F, What was the range of these marks?

    Sorry for all the questions, had hundreds of these and stuck on a few of them
    You probably have a table of values for the standard normal distribution N(0,1). Now if X = N(52,24) you can normalize

    P(X<x)=P\left(\frac{X-52}{\sqrt{24}}<\frac{x-52}{\sqrt{24}}\right)=P\left(Z<\frac{x-52}{\sqrt{24}}\right)

    where Z is standard normal N(0,1). Now you look for the corresponding value in table...

    Using this you should be able to solve a-d.
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