Assume that blood pressure reading are normally distrubuted withy

Question

Assume that blood pressure reading are normally distrubuted with mean 120. A researcher wishes to select people for a study but wants to exclude the top and bottom 12 percent . What would be the upper and lower readings to qualify people to participate in the study

Answer 1

What is the standard deviation? Essentially what you are doing is using the z-table backwards and finding the range of blood pressures that leave off the bottom 12% and the top 12%. If you are using a standard z-table (which does area to the left of the z-value); locate the z-value that has 12% to the left. That will be the bottom z-value (it should be negative), the top z-value will be the opposite sign because the distribution is symmetric. Once you have the z-values, use the z=(x-mean)/standard deviation formula and solve for x (using both z-values). That will get you the answer.