1. Sample Means
Section 9.3

2. Note: Averages are less variable than individual observations
Averages are more normal than individual observations

3. Mean and Standard Deviation
x bar = 
x bar = /n
Only use the standard deviation if the population is at least 10 times as large as the sample

4. Central Limit Theorem
Draw an SRS of size n from any population whatsoever with mean  and finite standard deviation . When n is large, the sampling distribution of the sample mean x bar is close to the normal distribution N(, /n) with mean  and standard deviation /n.
How large n has to be depends on how “far” from normal a population is

5. Practice Problems Section 9.3 Chapter 9 Review pg. 525 #9.39-9.42