Flexography is a printing process used in the packaging industry. The process is popular, since it is cost-effective and can be used to print on a variety of surfaces (e.g., paperboard, foil, and plastic). A study was conducted to determine if flexography exposure time has an impact on the quality of the printing (Journal of Graphic Engineering and Design, Vol. 3, 2012). Four different exposure times were studied: 8, 10, 12, and 14 minutes. A sample of 36 print images were collected at each exposure time level, for a total of 144 print images. The measure of print quality used was dot area (hundreds of dots per square millimeter). The data were subjected to an analysis of variance, with partial results shown in the accompanying table.

a. Compute the missing entries in the ANOVA table.
b. Is there sufficient evidence to indicate that mean dot area differs depending on the exposure time? Use a = .05.

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df MS MS Source p-Value <.001 Exposure Error 3 .010 .029 140 Total .039 143