Sunday, November 14, 2010

Chapter 8.22

Chapter 8.22

Note we’re told that the distribution has a normal distribution. This is important because the sample size is only 25, less than 30. Use Excel to get the mean

a. 3.348
b. Use =confidence(0.05,2.287,25) to get the margin of error. This is 0.896 (rounded). So the Confidence Interval is 3.348 – 0.896 to 3.348 + 0.896 (finish it off yourself which in the formal answer in a test you MUST do).

Now, the question doesn’t specify whether you need to calculate the Margin of Error ‘by hand’. Let’s do that just for practice. Recall that the M of E for 95% is 1.96 * SE. Here the Standard Error --- SE --- is 2.287/5 = 0.457 (rounded). So the Margin of Error is 1.96*0.457 = 0.896. The same as when we used =confidence. Then you can get the Confidence Interval in the same way....

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