Question

A quality control inspector samples 40 screws from a machine, and calculates the average as 1.960, and standard deviation as 0.08. The machine is set to produce screws which are 2 inches long on average. If the screws produced are too long or too short, the machine is shut down for repairs. The machine is assumed OK until proven otherwise. (The population of the screw lengths produced by the machine is normally distributed.) Use α = 0.05

Calculate the test statistic. What is the conclusion of this test?

		test statistic = 3.16; evidence not convincing ... keep operating
		test statistic = -3.16; shut the machine down for repairs.
		test statistic = -2.50; shut the machine down for repairs.
		test statistic = 3.16; shut the machine down for repairs.
		test statistic = -3.16;  evidence not convincing ... keep operating

* I found the test statistic to be -3.16, but I do not know if the machines should be left operating. Please help.

Answer 1