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    90% Confidence Problem

    This is the question I am struggling with, it is from a set of practice questions but I am trying to understand how to do this for my upcoming exams, this question just confuses me.

    Charitable organisations depend on donations for support. One organisation is interested in estimating the average donation to within $25.00, with 90% confidence. From past experience it is known that individual donations have a standard deviation of $200. How many donor files should be chosen for review?

    Thanks in advance,
    Cate

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    Re: 90% Confidence Problem

    Quote Originally Posted by CateB9 View Post
    This is the question I am struggling with, it is from a set of practice questions but I am trying to understand how to do this for my upcoming exams, this question just confuses me.

    Charitable organisations depend on donations for support. One organisation is interested in estimating the average donation to within $25.00, with 90% confidence. From past experience it is known that individual donations have a standard deviation of $200. How many donor files should be chosen for review?

    Thanks in advance,
    Cate
    Hi Cate! I think this might help you get the wheels turning. What is the formula for a confidence interval and what is each part of the formula? Starting here will likely prove beneficial for you.

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