We would apply the empirical formula which states that approximately 95% of the data in a normal distribution fall within 2 standard deviations of the mean.
From the information given,
mean = 265
standard deviation = 17
2 standard deviations = 17 x 2 = 34
2 standard deviations to the left = 265 - 34 = 231
2 standard deviations to the right = 299
Thus,
Approximately 95% of pregnancies have lengths between 231 and 299 days
