A study was conducted in which 20 volunteers adopt a low-cholesterol diet for 3 months. The cholesterol level of subjects were measured at baseline and after 3-months. Suppose that we observe a mean difference in cholesterol level was equal to 20 mg/dL and a standard deviation of differences equal to 35 mg/dL.

[Note: Don't round too soon in the calculation. Report four decimal places in questions 1 and 2; round to two decimals for your final answer to question 3.]

Before calculating the 95% confidence interval, it is always a good plan to first identify the values for the key elements in the formula. From White (2020), we know that the formula for a confidence interval for a mean difference is:

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