00:01
In your question, we have a simple random sample of 60 items.
00:04
It resulted in a mean of 80, population standard deviation of 15.
00:09
We're to compute a 95 % confidence interval.
00:13
So the way we create a confidence interval is take our statistic plus or minus, our margin of error, which is made up of a critical value that's based on your confidence level times standard error.
00:33
Now for us, our statistic is the x bar, plus or minus, our critical value.
00:40
We are being asked for a 95 % confidence interval.
00:44
That symbol is given the z star symbol, but we want to know that that 95 % confidence leads us to a z star of 1 .96.
00:56
That's something you really want to have memorized.
00:58
We do a lot of 95 % confidence intervals.
01:01
And then our standard error formula is take the popular.
01:05
Standard deviation divided by the square root of our sample size.
01:09
Okay, writing that out, we're going to have an 80 for our sample mean plus or minus 1 .96 for our critical value times 15 divided by the square root of 60...