Chapter20 - Chapter 20 Testing Hypothesis About Proportions...

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Chapter 20 Testing Hypothesis About Proportions
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Chapter Example Ingots are huge pieces of metal that are made in a giant mold. They must be cast in one large piece for use in fabricating large structural parts for cars and planes. Airplane manufacturers insist that metal for their planes are crack free. If there are cracks, then the ingot must be made over which cost tens of thousands of dollars.
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(cont.) In one plant, only about 80% of the ingots have been free of cracks. The plant engineers tried out some changes to reduce the cracking rate. Since then, 400 ingots have been cast and only 17% of them have cracked. Should they declare victory or was it just mere luck? Other words, is the 17% we observe merely a result of natural sampling variability, or is this strong enough evidence that the true cracking rate is really below 20%?
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Hypotheses To answer a question like this, we test hypotheses about models. A hypothesis proposes a model for the world.
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Chapter20 - Chapter 20 Testing Hypothesis About Proportions...

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