The human gestation period length of pregnancy is 270 days w

The human gestation period (length of pregnancy) is 270 days with a standard deviation of 9 days and is approximately Normlly distributed (assuming spontaneous labor). What is the probability that a randomly selected woman\'s gestation period will be between 261 and 279 days?

Solution

To the left of 261 :

z = (261 - 270)/9 = -9/9 = -1

Looking at the z-table for -1, the probability to the left will be 0.1587

P(x < 261) = 0.1587

To the left of 279 :

z = (279 - 270) / 9 = 9/9 = 1

Looking at the z-table for 1, the probability to the left will be 0.8413

P(x < 279) = 0.8413

So, P(261 < x < 279) = 0.8413 - 0.1587 = 0.6826 ---> ANSWER