Question 740331: When a person’s blood pressure is taken, two measurements are reported; for example, 120/65 (‘120 over 65’). The higher reading is known as the systolic blood pressure. For healthy people between 15 and 44 years of age, the systolic blood pressure (in mm Hg) is thought to be normally distributed with mean 125 and standard deviation 10. Throughout this question, we consider only healthy people between 15 and 44 years of age.
What reading is exceeded by only 20% of the systolic blood pressures of healthy people between 15 and 44 years of age?
(I got stuck on this question in my assignment and tried different distributions to end up back to the beginning. Can you guide me in the right direction)
Answer by rothauserc(4718)   (Show Source):
You can put this solution on YOUR website! Given a normal distribution with mean 125 and standard deviation 10 we are asked the following question
What reading is exceeded by only 20% of the systolic blood pressures of healthy people between 15 and 44 years of age?
this means the probability(P) is (X>x) = .2 and P(Z>z) = .2 where z = (x - mean) / standard deviation
since z is positive, to use the table for z we look at probability of Z less than z = .8 and
we see that the corresponding z value for .8 is .84, remember that the column values are the probabilities and the closest probability is .79955 which corresponds to a z value of .84
to find x from z we use z = (x - mean) / standard deviation
x = z*standard deviation + mean = .84*10 + 125 = 133.4
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