In the laboratory analysis of samples from a chemical process, five samples from the process are analyzed daily. In addition, a control sample is analyzed twice each day to check the calibration of the laboratory instruments.

a. How many different sequences of process and control samples are possible each day? Assume that the five process samples are considered identical and that the two control samples are considered identical.

b. How many different sequences of process and control samples are possible if we consider the five process samples to be different and the two control samples to be identical?

c. For the same situation as part (b), how many sequences are possible if the first test of each day must be a control sample?