Injection molding. To improve the quality of molded parts, companies often test different levels of parameter settings to find the best combinations. Injection molding machines typically have many adjustable parameters. One company used three different mold temperatures (25, 35, and 45 degrees Celsius) and four different cooling times

(10, 15, 20, and 25 minutes) to examine how they affect the tensile strength of the resulting molded parts. Five parts were randomly sampled and measured from each treatment combination.

a) Is this an experiment or an observational study? Explain.

b) What is the response variable?

c) What are the factors?

d) How many treatments are involved?

e) State the hypotheses (in words, not symbols).