00:01
So here we're looking for a 90 % confidence interval given x bar is 73 .8, s is 12 .2, and n is 741.
00:09
Where i'll note that for a confidence interval here, we have that it would be given by x bar plus or minus z for 0 .05 times s over the square root of the sample size.
00:22
Now z of 0 .05 is going to give us a value of 1 .645, and having that, we have that, we have a value.
00:30
Have basically everything we need to just go directly to the point of calculation.
00:35
So at the lower end, we'd have 73 .8 minus 1 .645 times 12 .2 divided by the square root of 741.
00:46
Oh, pardon me.
00:48
I've made a mistake here, particularly, and i'll just specify my mistake.
00:54
That is that we do not want to use a z score here.
00:58
In fact, we want to use a t score.
01:01
Because we don't have the population standard deviation.
01:05
We only have the sample standard deviation...