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A factory that manufactures screws is performing a quality control experiment. Each object should have a length of no more than 12 centimeters. The factory believes that the length of the screws is less than this value and measures the length of 70 screws. The sample mean screw length was 11.91 centimeters. The population standard deviation is known to be $\sigma=\mathbf{0 . 2 3}$ centimeters.

What is the null hypothesis? Select
What is the alternative hypothesis?
Select

Step 1 ：The null hypothesis in a statistical test is a statement that the observed data result from a chance variation alone. In this case, the null hypothesis would be that the mean length of the screws is equal to 12 centimeters.

Step 2 ：The alternative hypothesis is a statement that contradicts the null hypothesis. It is what you might believe to be true or hope to prove true. In this case, the alternative hypothesis would be that the mean length of the screws is less than 12 centimeters.

Step 3 ：Final Answer: The null hypothesis is: The mean length of the screws is equal to 12 centimeters. The alternative hypothesis is: The mean length of the screws is less than 12 centimeters.