The manufacturer of Boston and Vermont asphalt shingles constructed control charts and analyzed several quality characteristics. One characteristic of interest is the strength of the sealant on the shingle. During each day of production, three shingles are tested for their sealant strength. (Thus, a subgroup is operationally defined as one day of production, and the sample size for each subgroup is 3.) Separate pieces are cut from the upper and lower portions of a shingle and then reassembled to simulate shingles on a roof. A timed heating process is used to simulate the sealing process. The sealed shingle pieces are pulled apart, and the amount of force (in pounds) required to break the sealant bond is measured and recorded. This variable is called the sealant strength. The file Sealant contains sealant strength measurements on 25 days of production for Boston shingles and 19 days for Vermont shingles.
For the 25 days of production for Boston shingles,
a. Construct a control chart for the range.
b. Construct a control chart for the mean.
c. Is the process in control?
d. Repeat (a) through (c), using the 19 production days for Vermont shingles.