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Thread: deciles

  1. #1
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    Women's weights are normally distributed with a mean of 143 lb and a standard deviation of 29lb. Find the third decile, D3, which separates the bottom 30% from the top 70%.

    I tried doing the z=(y-mean)/std. deviation, but it did not work for me. We haven't done anything with these in class and I can't find any examples in my book. Please help!

  2. #2
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    JohnM's Avatar
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    You need to look up the z value in the z-table, not compute it. You should be able to locate the z-value that separates the bottom 30% from the rest --> it should have a proportion of the area equal to 0.30. Hint: it will be negative.

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