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# Confidence Intervals Worksheet Use your TI/84 calculator to practice finding confidence intervals for a population mean and a population proportion!...

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Confdence Intervals Worksheet Use your TI/84 calculator to prac±ce fnding confdence intervals For a popula±on mean and a popula±on propor±on! First review the ±ollowing worked examples: 1. Example o± a Confdence Interval ±or the mean, µ, o± a populaTon with a known: Suppose a random sample oF 240 credit card bills showed an average balance oF \$1250. Also assume that the popula±on standard devia±on is \$350. ²ind a 95% confdence interval For the popula±on mean credit card balance. To access the confdence interval choices, press STAT and select ²ES²S . The confdence interval choices are Found in items 7 through B. Select 7:ZInterval because the popula±on standard devia±on, σ , is known. In this example, summary sta±s±cs are given, so select the STATS op±on For input. Enter the value oF σ , the value oF ´ x and the sample size n . Use 0.95 For the C-Level. Highlight Calculate and press ENTER. 2. Example o± a Confdence Interval ±or the mean, µ, o± a populaTon with an unknown: In a test oF an exercise program that is designed For weight loss, 40 individuals par±cipated in a randomized trial to see how e³ec±ve the program is. A´er one month in this exercise program, the mean weight loss was Found to be 2.1 lb, with a standard devia±on oF 4.8 lb. ²ind a 95% confdence interval For the mean weight loss oF all adults who Follow the exercise program For weight loss. To access the confdence interval choices, press STAT and select ²ES²S . The confdence interval choices are Found in items 7 through B. Select 8:²Interval because the popula±on standard devia±on, σ , is unknown. In this example, summary sta±s±cs are given, so we will select the STATS op±on For input. We enter the value oF ´ x , s and n .Use 0.95 For the C-Level. Highlight Calculate and press ENTER.
3. Example of a ConFdence Interval for a populaTon proporTon, ^ p : The local NPR sta±on of a major city in the mid-west wants to Fnd the percent of its listening popula±on that gives dona±ons to the sta±on. 360 randomly selected listeners were surveyed, and it was found that 145 listeners made contribu±ons to the sta±on. ²ind a 95% conFdence interval for the propor±on of all listeners in that city who also made dona±ons to the sta±on. To Fnd a conFdence interval for a propor±on, press the S±A± key and use op±on A:1-PropZlnt under ±ES±S . No±ce that the normal z-distribu±on will be used. The sample size needed to construct a conFdence interval for ^ p with margin of error m: n = ^ p ( 1 ^ p )[ z m ] 2 if ^ p is available. n = 0.25 [ z m ] 2 if ^ p is unavailable.
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Confidence Intervals Worksheet
Use your TI/84 calculator to practice finding confidence intervals for a population mean and a population
proportion! First review the following worked examples:
1....

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