00:01
In this question, we're being asked about, we're estimating the mean number of hours that high school students spend watching tv, and we're interested in a margin of error of 0 .35, three, five hours.
00:15
Past studies suggest that a population interviation of sigma equals 1 .2 hours is reasonable, and so it asks if we wanna do a 95 % confidence interval, what is the sample size? remember that the margin of error, the formula you should know, is that it's z, some kind of multiplier for our confidence interval width, times sigma over root n.
00:38
The z, this z for a 95 % confidence interval is 1 .96, you should just know that, you can also get it by going and looking at the appropriate percentile of a normal distribution, a standard unit normal.
00:50
But anyway, right, we have 1 .96 sigma over root n, we know sigma, we want this to be equal to 1 .2, just moving things around, i get that the answer that we want is n equals that square, right? it's just through algebra...