## ← Exact Z-Scores - Intro to Inferential Statistics

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Showing Revision 5 created 05/24/2016 by Udacity Robot.

1. So let's bring up the Z table. So here's our Z table, area under the normal
2. curve. And we want this probability here. Well first of all, if 95% is here and
3. the total area under the curve is 100%, then that means 2.5% is in this tail and
4. 2.5% is within this tail. So we want to find out what this Z value is when
5. there's 2.5% less than that Z value. So let's bring up the Z table. We want this
6. gray region to be 0.025, or 2.5%, so if we try to find 0.25, we see that it's
7. here, at a Z value of negative 1.96. So this here is negative 1.96, and this
8. total area up until this Z value is 95% plus 2.5% which is 97.5%. So let's look
9. for 0.975, and we see that it's here, at positive 1.96. If we found that the Z
10. score here is negative 1.96, then since this is symmetric and mu is 0 standard
11. deviations from itself, then we know that this would be positive 1.96, but I
12. just wanted to show you, using the z table, how they're symmetric.