Probability and Statistics

Question

The systolic blood pressure of adults in the USA is nearly normally distributed with a mean of 121 and standard deviation of 17 .

Someone qualifies as having Stage 2 high blood pressure if their systolic blood pressure is 160 or higher.

a. Around what percentage of adults in the USA have stage 2 high blood pressure?

b. If you sampled 1100 people, how many would you expect to have BP> 160? Give your answer to the nearest person.

94   people

c. Stage 1 high BP is specified as systolic BP between 140 and 160. What percentage of adults in the US qualify for stage 1? 

Answer 1

Part a: First, find the z-score. This is the number of standard deviations 160 is above the mean, 121. So subtract and divide by 17. The z-score is (160-121)/17 or 2.29412. In a z-score table or calculator, you'll see that 1.0892% of people have blood pressure 160 or higher.

Part b: Find1.0892% of 1100, about 12 people.

Part c: The z-score for 140 is (140-121)/17 or 1.11765. Using the z-score calculator, you'll see that 13.186% of people have blood pressure 140 or higher. So, comparing this with the answer for part a, the percent of people with stage 1 is 13.186% - 1.0892% or about 12.1%.