Posted by Anand on .
The Frayed Nerves Anxiety Scale (FNAS) is used to measure the anxiety level of people on a scale from 0 to 1000. Four students were randomly chosen and given the FNAS before their second exam. Their scores were 700, 653, 740, and 707. The standard deviation sigma of the test is 40.
1. What is x bar?
2. What is the standard deviation of the mean?
3. What is the 95% confidence interval for x bar?
4. What is the 99% confidence interval for x bar?
5. How many students do you need to survey to get the plus or minus for the 95% confidence interval down to 20?
6. How about for the 99% confidence interval?

statistics 
PsyDAG,
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1. x = ∑x/n
2. SEm = SD/√n
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3. x ± 1.96 SEm
I'll leave the rest up to you.