00:01
So we're given a sample size of 250, and it is given to be a normal population, and we have a population standard deviation of 25, and they obtained a sample mean of 20 from those 250 values.
00:16
And in part a, we want to find the standard air of the mean, and the standard air of the mean is going to end up being the sample standard deviation divided by the square root of n.
00:28
So we're going to have a 25 divided by the square root of 250.
00:34
And let's see what we get there.
00:37
25 divided by the square root of 250.
00:40
I wish 250 were a perfect square.
00:42
Then it would come up kind of nicely.
00:44
But we have 1 .581 is roughly the standard a.
00:50
Then part b says, why can we find a 95 % confidence interval using the formula? and i don't have access to the book yet.
00:58
I just did that, but i'm assuming that this is the formula that they're referring to, and we're putting x bar plus or minus c times the standard air of the mean and x bars.
01:15
And we can use this because we have a normal population, and we have a known standard deviation...