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Exercises
1. Given that σ = 4 for a given population and the following sample data, find a 95%
confidence interval for µ.
24 31 31 34 18 22
2. Find a 90% confidence interval for µ given the following sample data from a normal
population:
87 97 67 88 97 73 81
3. In a random sample of 350 town residents, 230 of them have cable television. Find a 95%
confidence interval for the percentage of all town residents who have cable television.
4. A random sample of 450 soda cans of a given brand finds that the mean volume is 12.03
ounces with standard deviation 0.37 ounces. Find a 99% confidence interval for the average
Solutions
1. Since we are given σ we will use ZInterval. Enter the data into a list and then select data.
The 95% confidence interval is (23.466, 29.867).
2. Since we are not given σ we will use TInterval. Enter the data into a list and then select data.
The 90% confidence interval is (75.904, 92.667).
3. We use 1-PropZInt with x = 230 and n = 350. The confidence interval is (.60741, .70687).
4. Since we do not have σ and the sample size is large we use TInterval with Ë = 12.03 and
s = .37. The 99% confidence interval is (11.985, 12.075).
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