The highest possible z-score that is still in the lowest 80% of the systolic blood pressure distribution is z = . Use this z-score to determine x, the corresponding systolic blood pressure score. x = Systolic blood pressure between 120 and 139 is considered prehypertension. What percentage of senior citizens have systolic blood pressure in this range? (Round your z values to two decimal places before looking them up in the Standard Normal Distribution tool.) 23.18%