1. The ef ciency ratio for a steel specimen immersed in a phosphating tank is the weight of the phosphate coating divided by the metal loss (both in mg/ft2).

The article Statistical Process Control of a Phosphate Coating Line (Wire J. Internat., May 1997:

78—81) gave the accompanying data on tank temperature

(x) and ef ciency ratio (y).

Temp. 170 172 173 174 174 175 176 Ratio .84 1.31 1.42 1.03 1.07 1.08 1.04 Temp. 177 180 180 180 180 180 181 Ratio 1.80 1.45 1.60 1.61 2.13 2.15 .84 Temp. 181 182 182 182 182 184 184 Ratio 1.43 .90 1.81 1.94 2.68 1.49 2.52 Temp. 185 186 188 Ratio 3.00 1.87 3.08

a. Construct stem-and-leaf displays of both temperature and ef ciency ratio, and comment on interesting features.

b. Is the value of ef ciency ratio completely and uniquely determined by tank temperature? Explain your reasoning.

c. Construct a scatter plot of the data. Does it appear that ef ciency ratio could be very well predicted by the value of temperature? Explain your reasoning.