assume that blood pressure readings are normally distributed with a mean of 111 and standard deviation of 7. A researcher wishes to select people for a study but wants to exclude the top and bottom 10 percent. What would be the upper and lower readings to qualify people to participate in the study?

1 answer

the central 80% of the Z table lies within µ ± 1.282σ

So, plug in your numbers

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http://davidmlane.com/hyperstat/z_table.html