Suppose a group of statistics has been hired to answer the following question: What percentage of freeway and highway bridges in the United States were built more than 35 years ago?

(a) What is the population these statistics are studying?

(b) Give and example of stratified sampling for this population. Be specific.

(c) If the statistics chose their sample to be all of the individuals (from your answer to part (a)) located in the states of Oregon, Texas, and Tennessee, what type of sampling did they use?

(d) Here is a statement from www.infrastructurereportcard.org, published by the American Society of Civil Engineers: "the average age of the nation's ....bridges is currently 42 years."

Do yo think this is a Statistic or a parameter? Justify your answer.