Surface finishing for corrosion protection is usually the last manufacturing process that takes place before the sale or assembly of metal parts used in such things as automobiles and electrical appliances. This process is often done in shops that specialize in this procedure. A technique for applying bright zinc plating to steel is being tested. The variable under study is the thickness of the resulting coating in microns.

6.8 8.3 7.9 7.5 6.9

8.5 7.0 7.4 7.2 6.8

7.1 8.1 7.5 7.7 8.5

7.8 7.3 8.4 8.0 7.8

7.5 7.8 7.6 8.4 9.9

Question 1:

Construct a double stem-and-leaf diagram for these data. Comment possible distribution of this random variable

Question 2:

Construct a boxplot for these data, and identify the data point that is flagged as an outlier

Question 3:

Suppose that upon investigation it is found that the unusual data point discovered via your boxplot was for a strip that was inadvertently left in the coating solution longer than the procedure specified. What should be done with this data point ?

Question 4:

Construct a 95% confidence interval on the average thickness of the coating obtained via the new process

Question 5:

Would you be surprise to hear a claim that this average is 7.7 microns ?

Explain based on your confidence interval.