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Math Help - Hi, I'm a new user, and I need help with this Statistics problem

  1. #1
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    Hi, I'm a new user, and I need help with this Statistics problem

    Hi! This seems like a great place and everyone is so helpful sand I need some help so I came here. I'm in AP Statistics and this problem has me confused.
    So, here is the problem-

    Suppose 75% of all families spend more than $75 weekly for food, while 15% spend more than $150. Assuming the distribution of family expenditures on groceries is normal, what is the mean weekly expenditure and standard deviation?

    I have no idea how to start it or anything, thanks for the help guys!
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  2. #2
    Junior Member FelixFelicis28's Avatar
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    Re: Hi, I'm a new user, and I need help with this Statistics problem

    Quote Originally Posted by datpinecone View Post
    Hi! This seems like a great place and everyone is so helpful sand I need some help so I came here. I'm in AP Statistics and this problem has me confused.
    So, here is the problem-

    Suppose 75% of all families spend more than $75 weekly for food, while 15% spend more than $150. Assuming the distribution of family expenditures on groceries is normal, what is the mean weekly expenditure and standard deviation?

    I have no idea how to start it or anything, thanks for the help guys!
    From a table of cumulative values for the standardised normal distribution, you can find out what 'score' encompassed 75% of the area from the right and what score encompasses 15% of the area from the right.

    Then you can use the formula for standardising the normal distribution Z = \frac{X - \mu}{\sigma}. Simultaneous equations.
    Last edited by FelixFelicis28; September 20th 2013 at 03:27 PM.
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