00:01
We have been given some sample data.
00:02
Sample size n is 81.
00:05
The sample mean x bar is 1 ,400.
00:08
The sample standard deviation s is 218.
00:11
We want the margin of error at 95 % confidence.
00:15
So the formula for a 95 % confidence interval would be x bar, point estimate, plus and minus the margin of error, ts over root n.
00:26
So t is my critical value here.
00:29
It's not the only critical value, there's also z, and z is preferable.
00:33
We shouldn't use it here because sigma, the population standard deviation, is unknown.
00:38
So we should use t instead.
00:40
So this is what we're looking for, the margin of error.
00:43
We have s, we have n, we just need t.
00:46
We get that with three pieces of information.
00:49
First, we want the two tail value...