00:01
The lengths of human pregnancies from conception to birth varies according to a distribution that's approximately normal, with a mean 266 days, and a standard deviation of 16 days.
00:19
A study enrolls a random sample of 25 pregnant women.
00:26
Assuming all appropriate conditions are met, what is the probability that the average, so the average pregnancy length of the women in the study, is more than 268.
00:40
So we're trying to find the probability that our mu is greater than 268.
00:45
We're going to use a z score for this.
00:48
And we're going to go ahead, instead of having equal, again, we're trying to see when will this be greater than.
00:53
So i'm going to take 268 and subtract 266, and then i'll divide by that standard deviation i was given.
01:02
So z is greater than 0 .125.
01:10
So again, thinking about a picture...