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.