In a Red Cross sponsored laboratory study designed to investigate the average length of time blood can be stored safely in a blood bank in the United States, 20 freshly sampled 500 ml blood bags were monitored over a 6-month period. The results of this laboratory study showed that blood may be stored safely on average for 17 days.

(a) What is the target population in this study?

(b) Is 17 a statistic or a parameter? Explain.