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14. When to Use What: For each example below you should start to construct a confidence interval by identifying which distribution should be used to find the margin of error. The options are the z-distribution, the t-distribution, or neither. (a) a confidence interval for a population mean where n = 25, the population distribution is skewed, x = 13.7, and o is known to be 2.5. (b) a confidence interval for a population proportion where the sample size is 250, and the number of successes is 113. (c) a confidence interval for a population mean where n = 234, the population distribution is skewed, * = 1435, and o is known to be 234. (d) a confidence interval for a population mean where n = 15, the population distribution is normal, T = 130.7, o is unknown, and s=12.75