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Math Help - Help with a normal distribution question

  1. #1
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    Help with a normal distribution question

    The average amount spent by customers on a single visit to a particular supermarket is £42 with standard deviation £24. In addition, the amounts spent have a normal distribution.

    Giving your answers to 2 decimal places, use Excel to find the following:

    (a) What percentage of the supermarket's customers spend
    in excess of £45 in a single visit?

    (b) What percentage of the supermarket's customers spend
    less than £25 in a single visit?

    (c) What percentage of the supermarket's customers spend
    between £35 and £55?

    (d) The supermarket wishes to introduce a minimum amount
    for which credit cards may be used which enables 85% of customers
    to pay by credit cards. At what amount should this credit card
    minimum be set?

    I'm unsure how to answer this question any help would be really appreciated. Thanks
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  2. #2
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    Re: Help with a normal distribution question

    You need to use a table of normal distribution values to evaluate these.

    First you need to change to the standard normal distribution: if x has mean \mu and standard deviation \sigma then the z= \frac{x- \mu}{\sigma} has the standard normal distribution. If you are asked a problem like this, I suspect you have already been taught this and that your text has a table of the standard normal distribution in the back. If not there is one here: Standard Normal Distribution Table.
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  3. #3
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    Re: Help with a normal distribution question

    Quote Originally Posted by HallsofIvy View Post
    You need to use a table of normal distribution values to evaluate these.

    First you need to change to the standard normal distribution: if x has mean \mu and standard deviation \sigma then the z= \frac{x- \mu}{\sigma} has the standard normal distribution. If you are asked a problem like this, I suspect you have already been taught this and that your text has a table of the standard normal distribution in the back. If not there is one here: Standard Normal Distribution Table.
    Do you know how to do it in excel?
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  4. #4
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    Re: Help with a normal distribution question

    Quote Originally Posted by HallsofIvy View Post
    You need to use a table of normal distribution values to evaluate these.

    First you need to change to the standard normal distribution: if x has mean \mu and standard deviation \sigma then the z= \frac{x- \mu}{\sigma} has the standard normal distribution. If you are asked a problem like this, I suspect you have already been taught this and that your text has a table of the standard normal distribution in the back. If not there is one here: Standard Normal Distribution Table.
    Would you mind going through the answers with me? I would be so grateful.
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