00:01
Okay, so we want to find out the z score that separates some of these percentages.
00:05
So first one wants to know the z score for the highest 10%.
00:13
And if i draw that out with a normal curve, the highest 10 % is in the right -hand tail here.
00:22
That means there's 90 % in the left -hand tail.
00:26
Now, depending on what you use to find your z -scores, whether it's a calculator or a table, this method will differ.
00:35
I'm doing this based on using a table that shows me the area to the left.
00:39
If it shows me the area to the left, then what i'm looking for inside my table is 0 .9 and the closest z score to that, and when we do that, we get a z score of 1 .28.
00:52
Notice it's a positive z score because it's to the right of the mean.
00:57
Second one, pretty much the same thing, just a different percentage.
01:05
So if i want to do the same thing for the highest 30%, instead of making this a 10, now i'm going to make this a 10.
01:11
30 over here and that's going to make this a 70.
01:15
So again, depending on how you do this, i'm using a table.
01:19
You find a z score in this case of 0 .52.
01:29
Now if we want to find the lowest 40 percent, the lowest is on the left side.
01:43
So now i'm just switching it where i have 40 percent here.
01:47
And i don't even need the other side now because my table gives me to the left.
01:51
So i'm looking for an area of 0 .4 inside my table.
01:55
Because this is to the left of the mean, 50 % would be the mean...