# solution

Spreading rate of spilled liquid. Refer to the Chemical Engineering Progress (January 2005) study of the rate at which a spilled volatile liquid will spread across a surface, Exercise 11.30 (p. 658). Recall that simple linear regression was used to model y = mass of the spill as a function of x = elapsed time of the spill.

a. Find a 99% confidence interval for the mean mass of all spills with an elapsed time of 15 minutes. Interpret the result.

b. Find a 99% prediction interval for the mass of a single spill with an elapsed time of 15 minutes. Interpret the result.

c. Compare the intervals, parts a and b. Which interval is wider? Will this always be the case? Explain.

Exercise 11.30

Spreading rate of spilled liquid. Refer to the Chemical Engineering Progress (January 2005) study of the rate at which a spilled volatile liquid will spread across a surface, Exercise 2.130 (p. 132). Recall that a DuPont Corp. engineer calculated the mass (in pounds) of a 50-gallon methanol spill after a period of time ranging from 0 to 60 minutes. Do the data in the table below indicate that the mass of the spill tends to diminish as time increases? If so, how much will the mass diminish each minute?

Exercise 2.130

Spreading rate of spilled liquid. A contract engineer at DuPont Corp. studied the rate at which a spilled volatile liquid will spread across a surface (Chemical Engineering Progress, January 2005). Assume 50 gallons of methanol spills onto a level surface outdoors. The engineer used derived empirical formulas (assuming a state of turbulent-free convection) to calculate the mass (in pounds) of the spill after a period of time ranging from 0 to 60 minutes. The calculated mass values are given in the table. Is there evidence to indicate that the mass of the spill tends to diminish as time increases? Support your answer with a scatterplot.

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