confidence intervals: mean of 82, stand. dev. of 15; find...

[lmcmommy]

Could someone help me with this proplem?
I am totally lost.

4. A sample of the math test scores of 35 fourth-graders has a mean of 82 with a standard deviation of 15.
a. Find the 95% confidence interval of the mean math test scores of all fourth-graders.
b. Find the 99% confidence interval of the mean math test scores of all fourth-graders.
c. Which interval is larger? Explain why.

Thanks!

 

[tkhunny]

Re: confidence intervals

You should have a table of z-scores, or percentages of the Standard Normal Distribution. Have you such a table. Perhaps your calculator can give these?

Generally, greater confidence requires a wider interval.