help with basic stats
looking to get some help with a few questions. i know the answers but im not sure how to arrive at them. the section of this work deals with estimating intervals.
1. A sample size of 16 exams was taken. The average score was 76.2 with variance of 144. The 99% confidence interval for the true average exam score is??
67.359 to 85.041
how do we get this??
2. The sample size needed to provide a margin of error of 2 or less with a .95 probability when the population standard deviation equals 11 is???
117
explain....
3. It is know that the population variance equals 484. With a .95 probability, the sample size that needs to be taken if the desired margin of error is 5 or less is???
75
4. A random sample of 100 people was taken. Eighty of the people in the sample favored Candidate A. The 95% confidence interval for the true proportion of people who favors Candidate A is:
.0722 to .0878
5. A machine that produces a major part for an airplane engine is monitored closely. In the past, 10% of the parts produced would be defective. With a .95 probability, the sample size that needs to be taken if the desired margin of error is .05 or less is
139
can someone please help me with how to get to these answers. The section im reading on uses t-scores for some parts and z-score for some others and im lost on the formulas that will bring me to these answers.
thanks for your time
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