For each of the following statements, identify the number that appears in boldface type as the value of either a population characteristic or a statistic:
a. A department store reports that 84% of all customers who use the store's credit plan pay their bills on time.
b. A sample of 100 students at a large university had a mean age of 24.1 years.
c. The Department of Motor Vehicles reports that 22% of all vehicles registered in a particular state are imports.
d. A hospital reports that based on the 10 most recent cases, the mean length of stay for surgical patients is 6.4 days.
e. A consumer group, after testing 100 batteries of a certain brand, reported an average life of 63 hours of use.