In each case, you can reject H0 if P-value and fail to reject H0 (accept H0) if P-value >
Rejection region for level test:
Lower tailed test
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z -z
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Upper tailed test
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z z
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Two- tailed test
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z -z/2 or z z/2
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100(1-)% large sample confidence Interval:
Example 5: 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 300 are selected and 15 defective parts are found from machine 1 while 8 defective parts are found in the sample from machine 2. Is it reasonable to conclude that both machines produce the same fraction of defective parts, using the significance 0.05?
If this analysis done by hand
Sample sizes are large enough to satisfy the assumptions and it is a two-tailed test.
 =0.0383 where  =0.05 and  =0.0267
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