Question 740331
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