Blood pressure is a measure of the blood force against the walls of the arteries. the larger value represents the pressure when the heart contracts and pushes blood out (systolic), and the smaller value is the lowest pressure when the heart relaxes between beats (diastolic). Blood pressure that is consistently more than 140.90 mmHg is considered high, but for people with diabetes, 130/80 mmHg is considered high. normal blood pressure is below 120/80 mmHg. Consider a population of non-diabetic males with a mean systolic blood pressure of 115 mmHg, in which 19% are classified as having high blood pressure (i.e. more than 140 mmHg). Assume that the systolic blood pressure X is normally distributed.

a) Compute the standard deviation of the systolic blood pressure of X.

b) Compute the median, the first quartile and the third quartile of X.

Hint: The median of X is the value a for which P(X < a) = 0.5. The first and third quartiles of X are the values b and c for which P(X < b) = 0.25, respectively P(X < c) = 0.75.