00:01
Okay, and your question, you're working with the length of human pregnancies, and you're told that the mean for a human pregnancy is 266 days with standard deviation of 16.
00:12
You're also told that the distribution is approximately normal.
00:17
I've defined a variable.
00:18
I say let x equal the number of days of pregnancy, and i'm looking to find the probability that x, the pregnancy, is less than 258 days.
00:27
To do that, you can see i've built a normal distribution graph, 266, the mean at the center, 258, which is less than the mean, and we want to find the probability of being less than 258.
00:44
To start, i'm going to find a z score for this value.
00:48
And to do that, i would say z equals x is 258 minus the mean of 266, divided by the standard deviation of 16.
01:00
So 258 minus 266 and then divide that by 16.
01:08
That works out to negative 0 .5.
01:11
Now based on that value for a z, i'm pretty convinced that we should use a z table to find this answer...