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Math Help - mean & standard deviation -- been stuck for days

  1. #1
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    Unhappy mean & standard deviation -- been stuck for days

    A random sample of 50 new mothers was asked to estimate how much they spent on prenatal care. The results are present in the frequency distribution presented below.

    Amount spent on prenantal Care ($) Mothers (Number)
    0-99 2
    100-199 4
    200-299 8
    300-399 20
    400-499 16

    Total 50

    Calculate the mean amount spent on prenatal care AND using the short cut formula to calculate the standard deviation of the amounts spent on prenatal care.

    I got 229.5 for the mean but Im not sure if this is right, and the numbers im getting for standard deviation are all over the place.
    any help would be really appreciated. thanks
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  2. #2
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    Re: mean & standard deviation -- been stuck for days

    Quote Originally Posted by rensmom View Post
    A random sample of 50 new mothers was asked to estimate how much they spent on prenatal care. The results are present in the frequency distribution presented below.

    Amount spent on prenantal Care ($) Mothers (Number)
    0-99 2
    100-199 4
    200-299 8
    300-399 20
    400-499 16

    Total 50

    Calculate the mean amount spent on prenatal care AND using the short cut formula to calculate the standard deviation of the amounts spent on prenatal care.

    I got 229.5 for the mean but Im not sure if this is right, and the numbers im getting for standard deviation are all over the place.
    any help would be really appreciated. thanks
    from what ive learned, you just have to use the midpoint of each class.
    so your data will be as follows:
    49.5; 2
    149.5; 4
    249.5; 8
    349.5; 20
    449.5;16

    use that to find the mean and sd
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