An aluminum producer manufactures carbon anodes and bakes them in a ring furnace prior to use in the smelting operation. The baked density of the anode is an important quality characteristic, as it may affect anode life. One of the process engineers suspects that firing temperature in the ring furnace affects baked anode density. An experiment was run at four different temperature levels, and six anodes were baked at each temperature level. The data from the experiment are shown in Table 4E.6.

(a) Does firing temperature in the ring furnace affect mean baked anode density?
(b) Find the residuals for this experiment and plot them on a normal probability scale.
(c) What firing temperature would you recommend using?

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TABLE 4E.6 Baked Density Data for Exercise 4.39 Temperature(C 500 525 550 575 Density 41.8 41.9 41.7 41.6 41.5 41.7 414 41.3 41.7 416 41.7 41.8 41.2 410 41.6 419 41.7 41.3 41.0 40.6 418 412 41.9 41.5