116. No tortilla chip a cionado likes soggy chips, so it is important to identify characteristics of the production process that produce chips with an appealing texture. The following data on x  frying time

(sec) and ymoisture content (%) appeared in the article Thermal and Physical Properties of Tortilla Chips as a Function of Frying Time (J. Food Process.

Preserv., 1995: 175—189).

x 5 10 15 20 25 30 45 60 y 16.3 9.7 8.1 4.2 3.4 2.9 1.9 1.3

a. Construct a scatter plot of the data and comment.

b. Construct a scatter plot of the (ln(x), ln(y))

pairs (i.e., transform both x and y by logs) and comment.

c. Consider the multiplicative power model Y 

axbe. What does this model imply about the relationship between  ln(y) and  ln(x)

(assuming that e has a lognormal distribution)?

d. Obtain a prediction interval for moisture content when frying time is 25 seconds. Hint: First carry out a simple linear regression of on and calculate an appropriate prediction interval.