Question1: Explain why the critical value for a given confidence level when the population variance is not known is always greater than the critical value for the same confidence level when the population variance is known.

Question2: According to an investigation reporter members of Congress are coming under more scrutiny for “fact-finding” trips. Since 2000, members of Congress have made 6,666 trips paid for by private interests.  The trips were worth about $19.6 million.

[A] If the cost of the trips could be considered to have a normal distribution, determine the standard deviation of the cost of the trips. (Hint:  Recall the Empirical Rule)

[B] Choose a reasonable confidence level and calculate a confidence interval for the average cost of congressional “fact-facing” trips from the year 2000 until January 19, 2006.

[C] Calculate the average cost of these “fact-finding” trips.