00:01
So for our confidence interval, we know it's going to be in the form of x bar plus or minus z for proportion of alpha over 2 times our population standard deviation divided by the square root of our sample size.
00:15
We're told that we want a 99 % confidence level, which means that our alpha value is equal to 0 .01.
00:25
And therefore, alpha over 2 is going to be 0 .005, which means that we want to find either the negative value z .0 .005, proportion 0 .005 to the left, or the positive value, 0 .995.
00:42
So i'm going to bring up a cumulative probability table.
00:46
We want to find the point on the table, the sort of meat of it, that's closest to 0 .995.
00:52
We can see we're just below it at 2 .5, let's see here, at 2 .57 and just above it at 2 .58.
01:05
So we can conclude that our z score that we want here, 0 .995, is equal to 2 .575 roughly.
01:17
So having that, we can go back to our, we can go back to our expression up here...