Two different types of injection-molding machines are used to form plastic parts

Question

Two different types of injection-molding machines are used to form plastic parts. A part is considered defective if it has excessive shrinkage or is discolored. Two random samples, each of size 200, are selected, and 15 defective parts are found in the sample from machine 1 whereas 10 defective parts are found in the sample from machine 2. a) Is it reasonable to conclude that both machines produce the same fraction of defective parts, using alpha = 30.05? b) Find the P-value for this test. c) Find the P-value using Minitab and compare with b)

Explanation / Answer

The proportion of Yes or No responses for Observation 1 is 0.075. The proportion for Observation 2 is 0.05.

The Z-Score is 1.0328. The p-value is 0.30302. The result is not significant at p <0.05.

Z-score formula =[0.075-0.050] / sqrt[(0.0625* 0.9375 * 2/200] = 1.0328

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