Question 1203889
population mean is 270 days.
population standard deviation is 15 days.
test value = 257 days.


use z-score formula.
z = (x - m) / 15 becomes z = (257 - 270) / 15 = -.86667
z is the z-score
x is the test value
m is the mean
s is the standard deviation.


area to the left of z-score of -.86667 = .1931.
this means there is a 19.3% probability of a pregnancy lasting less than 257 days.
you would enter 19.3 as your solution is what i think based on the instructions.