SOLUTION: blood pressure readings are approximately normal with a mean of 120 and a standard deviation of 8. A researcher wishes to select people for a study but wants to exclude the top & b

Question 888795: blood pressure readings are approximately normal with a mean of 120 and a standard deviation of 8. A researcher wishes to select people for a study but wants to exclude the top & bottom 10%. What would be the upper and lower reading to qualify people to participate in the study? Please help I've spent almost an hour on this question
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
blood pressure readings are approximately normal with a mean of 120 and a standard deviation of 8. A researcher wishes to select people for a study but wants to exclude the top & bottom 10%. What would be the upper and lower reading to qualify people to participate in the study?
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Find the z-value with a right tail of 10%::
invNorm(0.9) = 1.2816
Find the z-value with a left tail of 10%::
invNorm(0.1) = -1.2816
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Lower limit:: x = -1.2816*8+120 = 129.16
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Upper limit:: x = +1.2816*8+120 = 130.25
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Cheers,
Stan H.
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