Question

A World Health Organization study of health in various countries reported that in Canada, systolic blood pressure readings have a mean of 121 and a standard deviation of 16. A reading above 140 is considered to be a high blood pressure. Assume that the distribution of systolic blood pressure is approximately normal. Let X denote the systolic blood pressure of a randomly selected Canadian. Use tables to find the third quartile of the distribution of the systolic blood pressure among Canadians, i.e. find x such that P(X<x)=0.75.

Answer 1

Given data,

mean () = 121

standard deviation () = 16

X be the systolic blood pressure of randomly selected canadian

To find X such that P(X<x) = 0.75

For this first find Z-score such that, P(Z<z) = 0.75 using Z-table we get Z = 0.67

We know,

= 0.67*16+121

X = 131.72

=> P(X<131.72) = 0.75

Thus, third quartile of the distribution of the systolic blood pressure among canadian is 131.72.